The taxman is writing to 24,000 people who may have falsely claimed on the government's coronavirus Self-Employment Income Support Scheme .
As the government scrambled to support the economy when the pandemic unfolded this year HM Revenue & Customs paid out £7.8bn to the 2.7m self-employed people claiming on the first tranche of the scheme.
But now the tax authority has confirmed it is writing to around 24,000 people to check if they claimed correctly.
HMRC said controls had been built into the scheme to stop fraudulent claims, but it was now pursuing post-payment compliance checks to recover money paid out where claimants had no active business.
During the pandemic the taxman had contacted about 100,000 people with information about claiming SEISS who had previously told HMRC they had stopped trading.
Of these 100,000, HMRC said 30,000 went on to make claims against the scheme, and about 6,000 of those have already been confirmed as trading businesses.
HMRC said: "We are now writing to around 24,000 people to ask them to check they claimed correctly.
"We have been able to confirm the remainder were trading so do not need to contact them.
"If they are trading and have claimed correctly, we may ask them for extra documentation to show this."
For those who had stopped trading but still made a claim, HMRC has set a deadline of November 20 to reply to its email or face a penalty.
The SEISS first launched in May as a mirror scheme to the government's furlough scheme and allowed claimants to receive grants covering as much as 80 per cent of their earnings during the pandemic, up to a maximum of £2,500 a month.
At the end of May the government announced it would extend the scheme, with those eligible able to claim a second and final grant worth 70 per cent of average monthly trading profits.
In August HMRC confirmed a number of self-employed individuals had been paid coronavirus support grants in error and some may have received an incorrect amount.
The taxman said the issue affected a small number of people who claimed from the self-employed scheme but confirmed it would not look to recoup any payments made in error.
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