Sir Ian Blair quits the Met

Britain's most senior police officer resigned tonight after a crisis meeting with the Mayor yesterday afternoon.

The Standard has learned that Mr Johnson, who took control of the Metropolitan Police Authority yesterday, told him he had reached "the end of the line" and should consider his options.

Events unfolded with dramatic speed today. Sir Ian told Deputy Mayor Kit Malthouse this morning before informing Home Secretary Jacqui Smith. Sir Ian told her he had to go, because the Mayor had effectively said he could no longer work with him.

The Met Commissioner offered to walk out immediately - but Ms Smith asked him to stay for a few months. They agreed he would leave in early December, more than a year earlier than the expiry of his contract in February 2010.

Sir Ian, 55, is understood to have negotiated a big severance payment, and is entitled to a gold-plated pension after more than three decades of service as a police officer. He was on a salary of £240,813.

In a statement tonight he was not expected to attack Mr Johnson personally, but his friends were making clear he felt bitter he had not been given more public support during recent allegations of impropriety involving contracts.

Labour ministers were in angry mood and planning to launch a political attack on Mr Johnson's handling of the matter.

But sources close to the Mayor said they had lost confidence in Sir Ian's ability to run day-to-day policing. "The Mayor has felt with growing anxiety over recent weeks that various issues surrounding Sir Ian became a distraction for the organisation," one said.

From Scotland Yard, a source said: "The Mayor effectively said he could not work with him. [Sir Ian] had no choice. The Mayor wanted a change of leadership."

Mr Johnson suggested Sir Ian should go the day he took direct control of the Metropolitan Police Authority. He is due to chair his first meeting on Monday. There have been rumblings in Conservative circles for several months that the Mayor was keen to oust Sir Ian. Publicly, Mr Johnson pointedly said that he believes the Mayor should have the power to hire and fire London's police chief in future.

Deputy mayor Kit Malthouse was accused of plotting to remove Sir Ian in July when leaked emails revealed he demanded to know why Mr Johnson could not remove the Met chief from his post while the contracts investigation was under way.

Former mayor Ken Livingstone gave strong support to Sir Ian during a string of controversies, including the Forest Gate shooting and the accidental killing of Brazilian Jean Charles de Menezes.

Sir Ian's friends are angry that he did not have the same support from Mr Johnson. One said: "The Mayor's office has been quiet during a string of unpleasant allegations, some of which may have involved dirty tricks."

The crisis comes after a series of controversies, ranging from questions about contracts awarded by the Met to Sir Ian's handling of the death of Mr de Menezes.

One allegation, that he awarded a £150,000 contract to Impact Plus, a company owned by his friend and skiing partner Andy Miller, had already prompted an investigation by the Metropolitan Police Authority.

Sir Ian is also facing claims of racial, religious and age discrimination against Britain's most senior Asian policeman, Met Assistant Commissioner Tarique Ghaf fur, who has launched an employment tribunal case against him.

And he faced renewed pressure of the de Menezes shooting at Stockwell tube station in July 2005 with the start last week of an inquest, which is expected to lead to fresh criticism. The Met has already been convicted over the killing under health and safety legislation.

Senior officers are believed to be working on a plan in which Deputy Commissioner Sir Paul Stephenson takes the top role with Assistant Commissioner John Yates as deputy.