Outstanding indebtedness from Carer's Allowance overpayments roseate to much than £250m past year, according to the government's spending watchdog.
The National Audit Office (NAO) said the fig had accrued by £100m since 2018/19.
Charity Carers UK said the study was "further grounds of a breached strategy that is failing unpaid carers".
The authorities launched an autarkic reappraisal of overpayments successful October, aft immoderate carers were forced to wage backmost thousands of pounds leaving galore successful fiscal hardship.
The Department for Work and Pensions (DWP) paid £3.7bn successful Carer's Allowance to much than 900,000 claimants past year, according to the NAO report.
If idiosyncratic spends astatine slightest 35 hours a week caring for idiosyncratic with an unwellness oregon disablement they whitethorn beryllium eligible for the allowance, which is presently £81.90 a week.
To qualify, idiosyncratic indispensable not gain much than £151 per week. The threshold volition emergence to £196 a week from April.
If a carer earns conscionable a lb supra this fig determination is nary taper complaint and they are nary longer eligible for immoderate payment.
The NAO said this created a "cliff-edge", meaning important overpayments tin physique up quickly.
Claimants are required by instrumentality to pass the DWP promptly if their circumstances change.
But the section has faced disapproval for failing to forestall overpayments, contempt its systems flagging erstwhile a claimant is earning excessively much.
Some carers person told the BBC they were unaware they had exceeded the threshold until being informed years later, erstwhile the sums had tally into thousands of pounds.
Claimants earning supra the permitted bounds made up 58% of caller overpayment cases past year.
Other reasons for overpayments see the claimant nary longer providing care, for illustration if the idiosyncratic being cared for has died.
Some 136,730 radical had outstanding overpayment indebtedness past year, an summation of 71% compared with 2018/19.
However, the NAO said the mean worth of caller overpayments identified by the DWP had fallen successful the past 4 years, suggesting they were being identified earlier.
The DWP seeks to retrieve each payment overpayments wherever it has a ineligible ground to bash so, unless it would origin fiscal hardship oregon would not beryllium outgo effective.
The section tin besides notation a lawsuit for prosecution if it considers an overpayment was fraudulent, which happened successful 54 cases past year.
As an alternative, it tin connection an "administrative penalty" of £350 oregon 50% of the overpayment, whichever fig is greater, up to a maximum of £5,000.
The fig of administrative penalties has fallen importantly successful caller years, from 774 successful 2018-19 to 75 successful 2023-24.
Meanwhile, determination has been an summation successful the usage of civilian penalties of £50 - with 30,129 imposed past year, up 50% from 2018-19.
The government-ordered review, which volition look astatine however to trim the risks of overpayment and however to enactment carers who person already accrued debts, is owed to study backmost by adjacent summer.
Hannah Walker, main enforcement of Carers UK, said immoderate recommendations from the reappraisal should beryllium implemented arsenic soon arsenic possible.
Dominic Carter, manager of argumentation and nationalist affairs astatine Carers Trust, called for a "complete overhaul" of the allowance system, describing it arsenic "overly complicated" and "outdated".
Minister for Social Security and Disability Sir Stephen Timms, said: "This study sets retired the standard of the situation and underlines the value of our autarkic reappraisal into overpayments truthful we tin marque the strategy fairer for thousands of selfless carers.
"Carers merit to beryllium supported, which is wherefore we are boosting the net threshold, benefiting much than 60,000 people, portion our reappraisal volition get to the bottommost of the occupation truthful we tin support carers from unfair indebtedness and support taxpayers' cash."