BRITAIN’S most senior police officer has been put on notice that he faces being axed unless he dramatically cuts crime.

The warning was delivered at a meeting between Boris Johnson, the new London mayor, and Sir Ian Blair, the Metropolitan police commissioner.

In his acceptance speech yesterday, Johnson spoke of the “dreadful scourge” of knife crime and gang culture in the capital.

The new mayor, who has made no secret of his concern at Blair’s performance, is ready to force a showdown with the home secretary, Jacqui Smith, over the Met commissioner’s position. He has told Tory colleagues he will demand that Smith fires Blair if significant progress is not made in cutting violent and petty crime.

Johnson also warned his staff will use the first days of the new administration to expose any evidence of corruption linked to defeated Ken Livingstone’s regime.

He said: “I imagine there are shredding machines quietly puffing and panting away in various parts of the building . . . Heaven knows what we shall uncover in the course of the next few days.”

In his rambling debut speech, Johnson also signalled he would not tolerate officials who begrudged the Tory victory, saying: “If there are any dogs in the manger, then I will have those dogs humanely euthanased.”

Johnson met Blair for a private briefing yesterday, when the Met chief was warned he must deliver or quit. The new mayor has already signalled his desire to remove Blair, setting the scene for a battle of wills with Labour.

He does not have the power to sack Blair, who is appointed by the home secretary. However, he is expected to assume the chairmanship of the Metropolitan Police Authority, which could hold a motion of no-confidence in the commissioner.

A senior Johnson aide said: “If Blair does not have the confidence of the mayor, the position of the Met commissioner is in doubt. The problem with Ian Blair is that he is not a policeman’s policeman. He is more interested in getting all the boxes ticked, in meeting targets than actually fighting crime.”

Tory MPs say Smith will have “no moral authority” to refuse to sack Blair. Mark Field, MP for the Cities of London and Westminster, said: “Ian Blair’s position may not technically be in Johnson’s hands, but he has a mandate from 1.2m people. Jacqui Smith will find it very difficult indeed to stand her ground if Johnson wants him out.”

Speaking after he was sworn in, Johnson pledged to “lead the fightback” against crime. The ceremony at City Hall came just hours after another boy was found stabbed to death in south London — the latest victim of a wave of knife crime among young people in the capital.

Johnson said: “I cannot help but remind you that another teenager — a 15-year-old — tragically lost his life to knife crime in this city and I do think that it’s time that we lead the fightback against this dreadful scourge.”

Johnson won the mayoral contest with 1,168,738 first and second preference votes, compared with Livingstone’s 1,028,966 on a record turnout of 45%.

During the campaign, Livingstone faced repeated allegations that taxpayers’ money was abused during his regime. His equality policy adviser, Lee Jasper, quit amid claims he channelled £100,000 to a project run by a women he bombarded with sexually charged e-mails.

As Johnson prepared to take up office, a “lock down” was ordered at City Hall and the London Development Agency, amid fears that documents related to ongoing police investigations may be destroyed.

Johnson is also preparing to make a swathe of redundancies to streamline the administration at the Greater London Authority. “It’s high time we had a city administration that concentrated on value for money, and we will deliver that,” he said.

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