Self-employed environmental consultant Andy Charles has no idea how fraudsters were able to claim thousands of pounds from a government scheme in his name.
But his case is just the tip of the iceberg, the BBC's Money Box has found.
HM Revenue and Customs (HMRC) says up to £258m in grants for the self-employed could have been fraudulent or paid in error.
Mr Charles, from Exeter, only found out about the fraudulent claim when he put in a genuine one.
"My initial reaction was just complete shock really," he told the BBC. "The application process is quite long and includes a lot of personal details, so to come to the end and be told this payment had already been applied for was quite shocking... the mind boggles really."
Despite two fraudulent claims being made in his name, Andy was eventually able to get two grants from the Self-Employment Income Support Scheme (SEISS) paid out, which has helped him get through the tough economic times caused by the coronavirus pandemic.
However, he still has concerns about how his personal details were used by criminals to make the fraudulent claims.
"I'm still, in the background of my mind, a little bit worried about what else people can get into. So can they just get into my personal tax details, [or] is there anything else I'm not aware of?" he said.
"So some real big questions about how the online system works and how HMRC are dealing with this type of stuff at their end."
In documents seen by Radio 4's Money Box programme, HMRC says it estimates that 1-2% of all cases are bogus.
With £12.9bn allocated in 4.7 million grants, that would mean £258m could have been paid out in error or fraud.
HMRC says the system was designed to prevent large-scale fraud and is confident it has done so. SEISS is significantly smaller than its counterpart, the Job Retention Scheme, which placed millions of people on furlough.
It has faced criticism for excluding too many self-employed workers, but with the first grant alone worth up to £7,500, for many the scheme has been a lifeline.
But accidental overpayments or fraudulent claims made by criminals using someone else's name are thought to be two examples of how incorrect payments may have been made.
HMRC does say the figure is an estimate and should be treated with caution: "We built controls into the application process, including limiting eligibility for the scheme to those who already had a tax footprint with HMRC, to stop fraudulent claims and we're confident that we've prevented large amounts of fraud.
"Our post-payment compliance checks to recover money paid out are set to begin, with the focus on those who claimed despite having no active business."
Andrew Chamberlain from the Association of Independent Professionals and the Self-Employed, says the misallocation of government funds is always a serious matter.
"Here it's particularly concerning because this is grant money that could be helping the more than a million struggling self-employed people who are excluded from government support," he told the BBC.
"It's important to put this in context, however. When compared to the Bounce Back Loan Scheme, where £26bn has been lost from fraud or default, or the Job Retention Scheme, which has lost £3.5bn through default or error, these numbers are comparatively low."
He added that it was "clear" the government needed to address fraudulent SEISS claims.
"Doing so, and plugging the leaks particularly in the BBLS and JRS schemes, would allow it to divert much-needed support to the UK's forgotten freelancers and self-employed."
You can hear more on BBC Radio 4's Money Box programme by listening again here.
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