Reynolds admitted that the client had filed in the online self-assessment form incorrectly, which probably explained the massive overpayment, but he was still baffled as to how such a substantial amount of money could be paid out erroneously without any checks.

Reynolds makes a good point, especially when one takes into the account that the National Audit Office recently revealed that HM Revenue & Customs was encountering attacks on the self-assessment system from organised criminals.

In one fraudulent attack alone, the NAO estimated £34m in repayments had been made to criminals targeting self-assessment. Advisers said they were stunned by the fact that SA had been targeted, as it was a fairly straightforward process.

But should we be surprised, especially when one considers cases of overpayments such as the one put forward by Reynolds. If an honest taxpayer can receive a £17,000 overpayment from HMRC through a simple error, imagine the sums that could be fleeced by a gang of determined and resourceful criminals who want to take the taxman for us much as they can.

In its report, the NAO said that HMRC needed to improve its systems as they were unable to 'prevent or detect error and irregularities'.

HMRC would do well to take on that advice. Sorting out large incorrect repayments may be the best way to cut off any scams that have seized on self-assessment as a soft target.

Nicholas Neveling is a reporter on Accountancy Age