The head of HM Revenue and Customs is to be hauled before a parliamentary committee to explain the handling of the unexpected tax demands going out to 1.4 million people.
Dave Hartnett, permanent secretary at HMRC, was forced to apologise at the weekend for the demands, which ask taxpayers to pay an additional average £1,428 because of inaccuracies in the PAYE system.
He said he was "deeply sorry" after a wave of anger greeted his comment in a radio interview that "I'm not sure I see a need to apologise".
Today, the chairman of the influential House of Commons Treasury Committee, Andrew Tyrie, made clear that he wanted to subject Mr Hartnett to a grilling by the cross-party committee.
He suggested that HMRC may be forced to make further concessions to taxpayers.
Mr Tyrie welcomed the Treasury's decision to write off debts smaller than £300 - an increase from the previous threshold of £50.
He told BBC Radio 4's The World At One: "What may I think turn out to be a cock-up in the handling may result in the long run in greater concessions of that type than the Government would otherwise have needed."
The Treasury Committee will decide tomorrow whether to call Mr Hartnett to give evidence on the PAYE errors, which will also result in millions of taxpayers receiving rebates.
But Mr Tyrie left little doubt that he wants the chief taxman to face questions: "The handling of this has aroused great public concern, understandably. The explanations we have had have come in dribs and drabs through media interviews. There is a strong case for saying he should now give an explanation to Parliament.
"I will be raising the issue of whether he should appear before the Treasury Committee at our meeting tomorrow. I will listen to what colleagues tell me, but I think you can tell from the way I am saying this that I am not happy with the way this has been handled."
