MPs questioning the top lawyer at HM Revenue and Customs have taken the unusual step of making him swear an oath to tell the truth.

Members of the Commons Public Accounts Committee felt they had been unable to get answers from Anthony Inglese.

The session was part of an inquiry into tax deals negotiated by HMRC with Vodafone and Goldman Sachs.

Mr Inglese and HMRC Permanent Secretary David Hartnett admitted that mistakes had been made in the deal.

Last year, Vodafone agreed to pay £1.25bn in tax arrears, but was apparently not asked to pay interest.

The deal was uncovered by the Guardian newspaper and Private Eye, leading to protests outside Vodafone offices.

Goldman Sachs negotiated a deal with HMRC, which the committee said had saved the investment bank between £8m and £10m.

Committee chair Margaret Hodge questioned why HMRC appeared to have a special relationship with such big businesses that allowed them to do deals in a way that would not be possible for smaller businesses or individual taxpayers.

Lost bonus

Mr Hartnett had told an earlier hearing that he had been advised by an HMRC official that there was a "legal impediment" to charging interest.

He revealed on Monday that an official from HMRC had lost his bonus as a result of the deals.

"The error was taken into account on someone's annual appraisal," he said.

The committee asked if that meant the individual lost their bonus and he replied, "I think that is another way of putting it."

The committee made Mr Inglese swear an oath after he continually declined to answer questions on the grounds of taxpayer confidentiality.

The committee suggested that taxpayer confidentiality should be overruled by parliamentary privilege.

Parliamentary staff said that nobody had been asked to swear an oath by a parliamentary committee for more than a decade.

Appearing alongside Mr Hartnett was the most senior civil servant, Sir Gus O'Donnell, who announced the appointment of two new tax commissioners.