The Guardian reports: Britain’s tax authorities have given Goldman Sachs an unusual and generous Christmas present, leaked documents reveal. In a secret London meeting last December with the head of Revenue, the wealthy Wall Street banking firm was forgiven £10m interest on a failed tax avoidance scheme.

HM Revenue and Customs sources admit privately that the interest-free deal is “a cock-up” by officials, but refuse to say who was responsible.

Documents leaked to Private Eye magazine and published in full by the Guardian record that Britain’s top tax official, HMRC’s permanent secretary Dave Hartnett, personally shook hands on a secret settlement last December.

Hartnett is due to be questioned on Wednesday by the Commons public accounts committee. The leaked documents suggest that a previous PAC chairman, Edward Leigh, was misled when he was told it was illegal to reveal details of such cases to parliament.

Leaked legal advice from James Eadie QC, which the Guardian also publishes today, says the opposite. Hartnett has discretion to reveal such facts to the parliamentary watchdog, according to the advice.

Leigh said: “It just underlines the absurd culture of secrecy that still pervades Whitehall.”

Hartnett also refused to give the facts about Goldman Sachs to MP Jesse Norman on the Treasury committee last month, claiming disclosure would be illegal. He also refuses to brief ministers on the details.

The £10m Christmas gift for Goldman was the culmination of a prolonged attempt by the US firm to avoid paying national insurance on huge bonuses for its bankers working in London.

The sum was pocket change to Goldman, whose employees received $15.3bn (£9.5bn) in pay and bonuses last year. Its Wall Street head, Lloyd Blankfein, received $68m in 2008 and at the height of Britain’s banking crisis 100 London partners set their bonuses at £1m each. This level was considered a mark of restraint.