Ex Not Paying Maintenance? How Private Investigators Are Supporting Parents Failed by CMS

For most separated parents, child maintenance is not about them; it is money intended to contribute towards the everyday costs of raising their children. Yet in August 2026, BBC Panorama reported that parents dealing with the Child Maintenance Service (CMS) were being pushed to “breaking point”, describing battles to obtain payments, financial hardship and growing frustration with the system designed to ensure their children receive financial support.

The BBC's investigation is the latest indication that problems with child maintenance are affecting a significant number of families. The issue has also attracted considerable attention in Parliament. During a House of Commons debate in March 2026, one MP reported receiving 5,000 messages from parents across the country after speaking publicly about problems with the CMS.

The scale of the system itself is enormous. According to the latest official Child Maintenance Service statistics, at the end of March 2026 the Child Maintenance Service was managing approximately 810,000 child maintenance arrangements involving 730,000 paying parents and covering 1.1 million children.

For the overwhelming majority of those cases, there is no suggestion that somebody needs to be investigated. If your ex is not paying maintenance, there can be many reasons for that and a private investigator will not usually be the answer.

There is, however, a much smaller and more specific group of cases that we regularly encounter through our private investigation work: parents whose ex is not paying maintenance at the correct level because they believe their former partner is working, earning income or holding relevant financial interests that have not been declared to CMS.

These are not simply cases of “my ex isn't paying maintenance.” The concern is much more specific: “My ex has told CMS they are unemployed or earning very little, but I believe they are actually working. How can I prove it?”

That distinction is extremely important.

Child Maintenance Not Paying: When the Problem Is Undeclared Income

The Child Maintenance Service has to calculate maintenance using financial information available to it and, for most paying parents, that works. Government evidence submitted to Parliament has previously stated that CMS relies extensively on information from HMRC and DWP benefits data when assessing paying parents.

If somebody is conventionally employed through PAYE, their employer reports their earnings to HMRC. The more difficult question is what happens when the allegation is that the work itself isn't being declared.

Examples might include a parent who claims to be unemployed while regularly working for cash, somebody undertaking undeclared self-employed work, or a person whose declared income appears inconsistent with the work they are actually undertaking. If the income has not been declared, the very reason it may not appear in conventional financial records is also what can make it difficult for the other parent to prove.

CMS recognises this problem. Parents can report incorrect information where they believe a paying parent has not declared all of their income, has hidden income or has provided incorrect information about their circumstances. CMS also has a specialist Financial Investigation Unit (FIU) capable of investigating complex cases.

Getting a case to that point, however, can require something crucial: credible information.

Prove Ex Is Working: Turning Suspicion Into Evidence

“I know my ex is working – but how do I prove it?” is one of the most common problems parents bring to us.

They may know that their former partner leaves home early every weekday, have been told that they are working on a particular building site, know that they are working for a friend or family member, or have seen photographs on social media suggesting that they are working. Their children may even innocently talk about where their other parent goes to work.

Knowing something and being able to evidence it objectively, however, are two different things.

This distinction matters because specialist CMS investigations aren't automatically opened simply because one parent alleges that the other is hiding income. Parliamentary scrutiny of the CMS has highlighted the importance of credible information when cases are considered for referral to the Financial Investigation Unit.

CMS has also acknowledged receiving a significant number of income challenges, some of which can be speculative. This creates an understandable dilemma for a parent who genuinely believes their ex-partner is working while claiming to be unemployed: how do they turn that suspicion into credible information that CMS can actually investigate?

That is one area where a professional private investigator can potentially help.

Child Maintenance Investigation: How Many Cases Reach the FIU?

The numbers provide some important context. At the end of September 2024, CMS was managing approximately 750,000 arrangements, yet during that quarter only 300 cases were referred to the Financial Investigation Unit. There were also 875 investigations continuing from previous quarters, while 340 financial investigations were completed during the same three-month period.

Of those 340 completed investigations, 210 resulted in the maintenance assessment being changed — approximately 62%, according to a Department for Work and Pensions answer to Parliament.

It is important not to misrepresent these figures. They do not mean that hundreds of thousands of other CMS arrangements should have been investigated; most child maintenance arrangements will never require specialist financial investigation. What they do demonstrate is how comparatively unusual referral to specialist financial investigation is within a system managing hundreds of thousands of arrangements.

More recent Parliamentary scrutiny paints a similar picture. The House of Lords Public Services Committee's report, Reforming the Child Maintenance Service, reported that only 1,400 Financial Investigation Unit cases were completed during the entire year ending December 2024. The Committee also heard that these investigations can take around two years to conclude, while subsequent appeals can potentially add another two to four years.

For a child who should be benefiting from maintenance today, those timescales matter. Equally significant is the fact that 210 of 340 completed investigations in one reported quarter resulted in the assessment changing. Once cases containing credible concerns reach specialist investigation, those investigations can therefore uncover information significant enough to alter the maintenance calculation.

Unpaid Child Maintenance: Does This Mean CMS Is Failing Parents?

Comparing the number of financial investigations with the total number of CMS arrangements does not mean that every other case should be investigated, and suggesting otherwise would be misleading. However, it would be equally wrong to dismiss concerns about unpaid child maintenance simply because specialist investigations are intended to be exceptional.

The BBC's recent reporting gives a human perspective to the statistics, with parents describing the financial and emotional impact of trying to resolve problems through CMS. Parliament has heard similar concerns, including discussion of parents being pushed to breaking point, hidden income, lengthy disputes and difficulties securing maintenance. The House of Lords has subsequently examined the operation of CMS in detail.

The problem, therefore, isn't hypothetical. For the particular group of parents who believe an ex-partner is deliberately concealing work or income, there can be an additional hurdle: providing enough credible information for the allegation to be properly investigated.

Hiding Income From CMS: What If My Ex Is Working Cash in Hand?

Cash-in-hand employment is particularly difficult because there may be little immediately visible connection between the work somebody performs and the financial information available through conventional sources.

Imagine, for example, that somebody tells CMS they are unemployed but in reality leaves their home at 6:30am each morning, travels to a construction site, puts on work clothing and PPE, undertakes apparent construction work throughout the day and leaves the site at approximately 4:30pm. If the same pattern occurs repeatedly, a professional covert surveillance investigation can potentially document those activities objectively.

What surveillance cannot necessarily establish is how that person was paid. Seeing somebody working does not prove that they received £150 in cash at the end of the day, and that distinction is important.

Our role as private investigators is not to decide somebody's income, determine their child maintenance liability or accuse somebody of fraud. Our role is to establish and document facts. CMS can then decide what those facts mean.

Ex Hiding Income: Can a Private Investigator Prove My Ex Is Working?

Depending upon the circumstances, covert surveillance can establish compelling evidence of someone's activities and working pattern. An investigation might establish that a person regularly leaves home at times consistent with working hours, travels repeatedly to the same workplace or building site, wears identifiable work clothing or PPE, uses tools or commercial equipment, attends customers or different work locations, operates a commercial or branded vehicle, or follows a repeated working pattern over several days.

Instead of simply telling CMS, “I know my ex is working”, the parent may then be able to provide an independently prepared report containing dated and timed observations together with supporting photographic or video evidence.

For parents trying to prove an ex is working, this distinction is important. The private investigator establishes what can objectively be observed; CMS, not the investigator, determines whether that information warrants further investigation or affects the maintenance assessment.

CMS Has Investigative Powers That Private Investigators Don't

It is important to understand the distinction between a CMS financial investigation and a private child maintenance investigation.

Private investigators do not have special access to HMRC. We cannot simply look inside someone's bank account and we cannot obtain protected financial information because somebody's former partner asks us to.

The CMS Financial Investigation Unit, by contrast, has powers available to it and can request information from government bodies and financial institutions when investigating appropriate cases. The House of Lords' examination of the CMS specifically records the FIU's ability to request information from government and financial institutions to check the accuracy of a paying parent's disclosures.

This is why a private investigator should not be viewed as an alternative to CMS. We can potentially help address an earlier evidential problem: is there credible evidence that the paying parent's declared circumstances may not reflect what they are actually doing?

Where the answer is yes, that evidence can be supplied to CMS so that CMS can determine what further enquiries are appropriate.

What About Self-Employed Parents?

Self-employment and more complex financial arrangements can present additional difficulties. A straightforward PAYE employee generally has earnings reported directly to HMRC, whereas somebody who controls a business may have considerably more influence over how and when they receive income.

Parliamentary scrutiny has highlighted difficulties arising from self-employment and other methods by which the income available for a CMS calculation may not necessarily provide a simple picture of someone's financial circumstances.

CMS consequently has mechanisms that allow certain additional income to be considered. Depending upon the circumstances, these can include certain unearned income, rental income, dividends and interest, certain assets, additional earned income and diversion of income.

Diversion of income can arise where a paying parent has the ability to control the income they receive and diverts it elsewhere. These are complex matters, and evidence that somebody appears to be working does not automatically establish what their taxable income should be. Where the concern is that someone's declared circumstances simply do not correspond with their observable working activities, however, obtaining objective evidence may provide a starting point for further enquiries.

Can CMS Investigate Hidden Assets or Income?

Yes, in appropriate circumstances. CMS has processes for considering income that may not have been included in the original calculation, and its Financial Investigation Unit can investigate complex cases.

A parent can also ask CMS for a variation where certain additional income or financial circumstances should be taken into account. Official CMS guidance for receiving parents confirms that relevant categories can include rental income, dividends and interest, notional income from qualifying assets, certain earned income and diversion of income. The guidance also stresses that an application should contain as much information as possible.

This is another situation where professional investigation may assist. Depending upon the circumstances, open-source investigation can potentially identify business interests, property connections, commercial activity and other publicly or lawfully available information relevant to concerns about an ex hiding income.

Again, an investigator does not determine whether an asset should form part of a maintenance calculation. We establish information; CMS determines its significance.

Is It Legal to Hire a Private Investigator for a Child Maintenance Investigation?

This is one of the first questions many parents ask us. There is an understandable misconception that because an investigation is covert, it must somehow be illegal.

That is not the case.

Professional private investigation is a recognised activity in the UK, but investigators must comply with data protection, privacy and other applicable laws. In October 2024, the Information Commissioner's Office formally approved the Association of British Investigators UK GDPR Code of Conduct for Investigative and Litigation Support Services. The Code specifically addresses how professional investigators can comply with UK GDPR, including lawful bases for processing personal information, legitimate interests assessments and Data Protection Impact Assessments.

That does not give an investigator unrestricted powers. A professional investigation does not permit hacking someone's accounts, illegally accessing financial records, trespassing or placing cameras inside somebody's home. Investigations need to be justified, necessary and proportionate, but the fact that somebody has not consented to an investigation does not automatically make the investigation unlawful.

Can a Private Investigator Legally Follow and Film My Ex?

Covert surveillance can be conducted lawfully in the UK when it is carried out appropriately, but privacy still matters. Professional investigators therefore consider the purpose of an investigation, the information being sought, where observations take place and whether the proposed activity is necessary and proportionate.

Where surveillance is justified, observations conducted from lawful locations can provide an independent record of a person's activities, including photographic and video evidence where appropriate.

For a child maintenance investigation, the objective should not be to obtain as much private information about the subject as possible. It should be much narrower: to establish relevant evidence concerning the suspected undeclared working activity.

That distinction is fundamental to conducting professional and proportionate surveillance.

Can Private Investigator Evidence Be Given to CMS?

Parents sometimes assume that evidence gathered by a private investigator cannot be used because the person being investigated did not consent to it. That is not automatically the case.

CMS provides mechanisms for parents to report suspected fraud or incorrect information and to provide information supporting their concerns. Its approach to specialist financial investigations also places importance on credible information before appropriate cases are escalated.

A professionally prepared investigation report can therefore provide relevant information that a parent can submit to CMS. The ultimate decision remains with CMS; providing surveillance evidence does not automatically trigger a reassessment and does not mean CMS is obliged to accept the investigator's interpretation.

That is why a professional report should concentrate on facts rather than accusations.

What Does a Professional Surveillance Report Contain?

A properly prepared surveillance report should provide an objective chronology of what actually occurred. For example:

07:12hrs – The subject departed their residential address wearing dark work trousers and a high-visibility jacket.

07:46hrs – The subject arrived at a construction site and entered through the contractor entrance.

12:34hrs – The subject was observed undertaking activity on the site.

16:28hrs – The subject departed the construction site and returned to their vehicle.

Supporting photographs or video can accompany those observations.

Notice what the investigator does not say: “The subject is committing child maintenance fraud.” That isn't our determination to make. The evidence establishes the activity; CMS can investigate the financial implications.

Frequently Asked Questions About Hidden Income and Child Maintenance

1. How Can I Prove My Ex Is Working When They Tell CMS They're Unemployed?

Evidence of a repeated working pattern can potentially be obtained through lawful surveillance and open-source investigation. A professional investigation can document where a person travels, the activities they undertake and relevant patterns over a period of time. If you need to prove your ex is working, independently documented observations can be considerably more useful than simply reporting a suspicion.

2. What Can I Do If My Ex Works Cash in Hand?

You can report concerns about undeclared income to CMS. Where there is currently insufficient evidence to support your belief, a professional investigation may potentially establish evidence of the person's working activities.

3. Can I Report My Ex for Hiding Income From CMS?

Yes. CMS has a process for reporting suspected incorrect information, including circumstances where you believe a paying parent has failed to declare income. If you suspect your ex is hiding income, providing specific and credible information explaining the basis of your concerns is important.

4. What Evidence Does CMS Need to Investigate Undeclared Income?

CMS guidance indicates that Financial Investigation Unit referrals should be supported by credible information. That can include information concerning employment, lifestyle and other relevant evidence.

5. How Do I Get CMS to Investigate My Ex?

Provide CMS with accurate and specific information explaining why you believe the income or circumstances used in the maintenance calculation are incorrect. CMS determines whether specialist investigation is appropriate.

6. Can a Private Investigator Prove My Ex Is Working?

A private investigator can potentially obtain objective evidence demonstrating that somebody is undertaking activities consistent with employment or self-employment.

7. Can Surveillance Prove Cash-in-Hand Work?

Surveillance can potentially establish that somebody is regularly undertaking work. It will not necessarily establish how much they are being paid or whether payment is being made in cash.

8. Will CMS Accept Private Investigator Evidence?

CMS allows parents to provide information supporting allegations of incorrect circumstances or undeclared income. A professional investigation report can be submitted as supporting information, although CMS decides what weight to give the evidence and what action to take.

9. Can Surveillance Evidence Trigger a CMS Investigation?

Credible evidence of previously undeclared working activity may give CMS information upon which it can consider further enquiries or referral for specialist investigation. An investigation is not guaranteed.

10. Can CMS Reassess Maintenance Using New Evidence?

CMS can recalculate maintenance where appropriate when relevant income or circumstances are established to be different from those previously used.

11. Can CMS Backdate Unpaid Child Maintenance?

In some circumstances changes can take effect from an earlier date, but this depends upon why the calculation changed and the relevant CMS rules. Parents should ask CMS how any change would apply to their particular case.

12. What Happens If My Ex Lies to CMS?

CMS can investigate suspected incorrect information and, where appropriate, change a maintenance assessment.

13. How Does CMS Investigate Hidden Income?

Complex cases can be referred to the Financial Investigation Unit, which has powers to obtain information unavailable to private individuals or investigators, including information from certain financial institutions and government sources.

14. My Ex Is Self-Employed and Declares Very Little Income. What Can I Do?

You can challenge information where you have credible grounds to believe the figure does not properly reflect relevant income. Depending upon the circumstances, a CMS variation or further investigation may be appropriate.

15. How Does CMS Investigate Self-Employed Income?

CMS generally uses HMRC information but has processes for cases involving additional or disputed income. Complex cases can potentially be referred for specialist investigation.

16. Can Company Directors Hide Income From CMS?

Company directors can have more complex remuneration arrangements than conventional PAYE employees. CMS rules include mechanisms for considering certain additional income and diversion of income where the relevant conditions are met.

17. Can CMS Include Dividends in Child Maintenance?

Certain unearned income, including qualifying dividend income, can potentially be considered through the variation process.

18. What Is Diversion of Income?

Broadly, it concerns circumstances where a paying parent has the ability to control their income and diverts it to another person or purpose in a way relevant to the maintenance calculation.

19. Can CMS Investigate Hidden Assets?

Certain assets and income generated from assets can be relevant under CMS variation rules. The precise treatment depends upon the circumstances and applicable thresholds.

20. What Is a CMS Variation?

A variation is a mechanism allowing certain additional income, expenses or circumstances that are not included in the standard calculation to be considered.

21. Is It Legal to Hire a Private Investigator to Investigate My Ex?

Yes, private investigation itself is not unlawful. The investigator must have an appropriate lawful basis and conduct the investigation in accordance with applicable privacy, data protection and other laws.

22. Is It Legal for a Private Investigator to Follow My Ex?

Covert surveillance can be lawful when appropriately justified and conducted. Professional investigators should consider necessity, proportionality, privacy and data protection before undertaking surveillance.

23. Can a Private Investigator Legally Film My Ex Without Permission?

Consent is not necessarily required for every lawful investigative activity. However, where and how footage is obtained, its purpose, proportionality and the subject's reasonable expectation of privacy are important considerations.

24. Does My Ex Need to Consent to Surveillance?

Not necessarily. Lack of consent does not automatically make an investigation unlawful. A professional investigator must nevertheless establish an appropriate lawful basis for processing personal information and conduct the investigation proportionately.

25. Can I Legally Give Surveillance Evidence to CMS?

Where evidence has been lawfully obtained and processed for an appropriate purpose, relevant information can potentially be supplied in support of concerns reported to CMS. CMS will decide what significance to attach to that evidence.

Ex Not Paying Maintenance Because They Are Hiding Income?

There is an important distinction between an ex not paying maintenance and somebody who may be paying an artificially low amount because their declared employment, income or financial circumstances do not reflect reality.

We do not recover unpaid child maintenance, and we do not investigate somebody simply because they have stopped making payments. However, if your former partner has told CMS that they are unemployed or earning substantially less than you have genuine reason to believe is the case, professional investigation may be able to help establish objective evidence of their activities.

That could involve open-source research, background enquiries, asset investigation or, where necessary and proportionate, covert surveillance. The purpose isn't to harass a former partner or interfere with their private life; it is to answer a specific factual question: does the available evidence support your belief that they are actually working or that relevant financial circumstances have not been declared?

Where evidence is obtained, it can be documented objectively and supplied to you in a professional report with supporting photographs or video where appropriate. You can then provide relevant evidence to the Child Maintenance Service and ask it to consider whether further investigation or reassessment is warranted.

For parents who have spent months telling CMS “I know my ex is working”, independently documented evidence can transform that statement into something much more useful:

“Here is the evidence showing why I believe an investigation is necessary.”