David Cameron has come under fire from fellow Conservatives in the aftermath of the drawn-out controversy over Andrew Mitchell's foul-mouthed confrontation with Downing Street police.

In a blow to the Prime Minister, who had backed his chief whip to remain in post, Mr Mitchell finally quit on Friday night after realising the row had cost him his authority among Tory MPs.

The decision came at the end of a week of conversations with parliamentary colleagues in which many made clear they felt he had to go.

Yesterday Home Secretary Theresa May would not deny that she had been one of those telling him to resign, although hostility from a significant section of the newer 2010 intake of Tory MPs appears to have been as important to his decision as the views of Cabinet ministers.

Ministers hoped that Mr Mitchell's resignation would at last draw a line under the issue but criticism emerged yesterday of Mr Cameron's handling of the issue and of the sense that the Government is lurching from one poorly-managed embarrassment to another.

Mr Mitchell's resignation came hours after Chancellor George Osborne was accused of trying to sit in a first-class rail carriage with a standard ticket, and in the same week that Mr Cameron announced a fuel bill policy that his energy ministers appeared to know nothing about.

Conservative peer Lord Tebbit said the Government had allowed an impression of incompetence to set in.

Writing in The Observer, the Thatcherite former minister said: "This dog of a Coalition Government has let itself be given a bad name and now anybody can beat it."

He added: "The abiding sin of the Government is not that some ministers are rich, but that it seems unable to manage its affairs competently."