The taxman’s ability to recoup £1.5bn from Barclays customers in unpaid taxes has been put in doubt after HM Revenue & Customs revealed it was anticipating a much smaller haul from the four other banks it has subsequently won disclosure orders against.

HMRC estimated that the four offshore customer account disclosure orders it was awarded by the special commissioners last week could bring in only £275m, due to a new method of calculation.

The orders were won against four of the UK’s largest banks: Lloyds TSB, HSBC, HBOS and RBS.

The taxman said that its £275m estimate was generated by a 'revised methodology' that was more cautious than the one used in the landmark Barclays case it won last year.

A HMRC spokesman said that the Barclays figure had been calculated at the time as part of a rela-tively new methodology, while the figure for the latest disclosure orders had benefited from experience and evidence.

But HMRC said it believed it could still recover the £1.5bn.

‘We are not necessarily revising that figure,’ said the spokesman.

Grant Thornton tax partner Mike Warburton suggested that the Barclays estimate may have been deliberately inflated to help persuade the special commissioners to rule in HMRC’s favour.

There is also the possibility that a lower estimated haul for the other banks could make it easier to issue an ‘amnesty’.

Warburton questioned whether there was government appetite outside of the Treasury for an amnesty: ‘I think part of the problem is a battle between Treasury and others in government over any type of amnesty, so perhaps the numbers have been played down to make one more possible.’

Anne Redston, the CIoT’s personal tax specialist, said the biggest issue for HMRC was not whether it would rake back £1.5bn from Barclays, but how to trawl through the data for the hundreds of thousands of bank customers it now has in its possession. ‘I’m sure they’ll look to streamline the process, but HMRC has insisted there will not be an amnesty,’ Redston said.

With staff cuts beckoning, Redston said it was unlikely that HMRC would have armies of workers available to trawl through individuals’ details. ‘It would be helpful for HMRC to say something soon about its plans,’ she said.