A single mother missed out on £10,000 in child benefits as a result of government failings, a watchdog investigation has found.

The Department for Work and Pensions (DWP) missed “vital opportunities” to ensure that arrears totalling £10,018.27 were paid to a woman who was underpaid child maintenance for years, according to the Parliamentary and Health Service Ombudsman.

The woman, known only as Ms W, from London, was forced to give up her job in the legal sector after being diagnosed with an autoimmune disease and chronic pain condition in 2002.

Her child’s father, who owed thousands in unpaid child maintenance by this point, then went on to sell a property he owned in 2003.

The ombudsman said the Child Support Agency (CSA) – a branch of the DWP – failed to fulfil its duty to prevent the father from selling the property, and therefore did not retrieve the money that Ms W and her child should have received.

Its investigation found that despite there being several actions that the CSA could have taken to reclaim the money owed from the sale, it failed to do so.

The amount the father received from the sale of the property was significantly higher than the amount he owed Ms W in child support arrears – yet the mistakes made by the CSA meant that she and her child were left with nothing.

The ombudsman found that not only did Ms W suffer significant financial loss because of these failings, the stress caused by the experience also had a negative impact on her health and wellbeing, creating “distress, inconvenience and frustration”.

Following the investigation, the CSA was forced to apologise to the woman and pay her £10,018.27 in compensation for the child support she would have received but for the failings, plus interest; as well as £2,000 for the suffering caused to the woman due to its handling of the complaint.

The case was revealed as part of the watchdog’s first annual Ombudsman’s Casework Report​, which called for the legislation around complaints by individuals about the government and its agencies to be “changed swiftly” – describing it as “outdated”.

It concludes that public service failures affect people from all walks of life, yet many are prevented from accessing the service directly because they are required to refer their complaint to an MP first.

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Ombudsman Rob Behrens said: “What connects the varied cases in this report is that something has gone wrong with a public service. When people bring such cases to us we hold organisations to account – making sure they learn from mistakes so they are not repeated.

“We hope that, as is the case for the NHS, complaints about the UK government and its agencies can soon come to us directly rather than needing referral by an MP. The legislation governing this is outdated and should be changed swiftly.”

A DWP spokesperson said: “We introduced the Child Maintenance Service to replace the under-performing Child Support Agency, precisely because of failings such as those in this case.