Claims that Met officers fiddled £6m expenses hit embattled Blair

Shadow Attorney General adds to pressure on Commissioner amid Lawrence leak claim

The embattled Metropolitan Police Commissioner, Sir Ian Blair, faced fresh pressure to resign last night after Dominic Grieve, the shadow Attorney General, demanded his dismissal. Sir Ian had discredited Scotland Yard and lost the confidence of the public by "placing himself above the law" in an attempt to block an Independent Police Complaints Commission investigation into the shooting of Jean Charles de Menezes, Mr Grieve said.

In a letter to the Home Secretary, Jacqui Smith, he called on her to " act decisively" and replace Sir Ian with a "commissioner who can command public confidence". Mr Grieve accused Sir Ian of acting in "clear breach of his statutory duties and the will of Parliament".

The pressure on Sir Ian intensified last night after it was revealed that an internal inquiry was looking into allegations that £6m in expenses had gone missing over the past three or four years.

Detectives are alleged to have paid for holidays, jewellery and luxury goods such as flat-screen televisions on American Express cards issued by the force for booking accommodation and flights during investigations. The Met's professional standards unit is expected to speak to hundreds of officers and examine 3,000 credit card accounts.

Scotland Yard confirmed that two detectives had been arrested on suspicion of theft. They are believed to be from the SO15 counter-terrorism squad. Lord Harris, chairman of the Metropolitan Police Authority's corporate governance committee, told the News of the World: "The slowness of the Met's leadership to respond to recommendations from their internal auditors has been a source of constant annoyance to me. We have been tightening up these processes and that is why these abuses are being uncovered."

Mr Grieve's call is the latest in a succession of demands for Sir Ian's resignation. He suffered a vote of no confidence from the London Assembly last week after his force was fined £175,000 at the Old Bailey for endangering the public with a series of "fundamental failures" during the botched operation in which the innocent Brazilian was mistaken for a potential suicide bomber and shot dead. Ms Smith has insisted repeatedly that she has full confidence in the Commissioner, and Gordon Brown went out of his way to praise Sir Ian's "creditable" achievements.

In an interview for BBC1's Andrew Marr programme, to be broadcast today, the London Mayor, Ken Livingstone, said: "We are all pretty determined we are not going to have a media campaign drive a Commissioner from office... We have never had that before and we cannot allow it."

Meanwhile, senior Scotland Yard officers denied claims that the Met leaked new information about the Stephen Lawrence murder case last Wednesday to divert attention from Sir Ian's difficulties. The claim was made by Michael Mansfield QC, who acts for Doreen and Neville Lawrence, who were " disturbed and angered" by the leak. Police sources said there was " absolutely no evidence" of a leak.