ANDREW Mitchell, the Tory chief whip who allegedly called a policeman a "pleb", has resigned tonight.

He denied insulting the policeman after he was refused permission to cycle through the main gates of Downing Street on September 19

The resignation came amid rumours that he had lost the backing of colleagues in the Whips' office - lthough backbenchers were broadly supportive at a meeting earlier this week.

Mr Mitchell admitted that the episode had been ''upsetting and damaging'' for the party, thanking David Cameron for his ''loyalty''.

And for the first time, he publicly spelled out his version of the incident.

''I have made clear to you - and I give you my categorical assurance again - that I did not, never have and never would call a police officer a 'pleb' or a 'moron' or used any of the other pejorative descriptions attributed to me,'' he wrote.

''The offending comment and the reason for my apology to the police was my parting remark, 'I thought you guys were supposed to f****** help us'.

''It was obviously wrong of me to use such bad language and I am very sorry about it and grateful to the police officer for accepting my apology.''

The timing of the departure is likely to draw allegations of cynicism, coming as Chancellor George Osborne faces widespread mockery over apparently trying to travel first class on a train with a standard ticket.

Mr Mitchell's fate is believed to have been sealed on Wednesday, when after a tumultuous PMQs deputy chief whip John Randall reportedly had to be talked out of quitting in protest at his determination to cling on.

In his letter of reply, Mr Cameron said he ''understood'' why he was resigning, adding: ''I regret this has become necessary.''

According to the 442-word police log, Mr Mitchell called officers "f****** plebs" and told them to "learn your f****** place".

Paul McKeever, chairman of the Police Federation of England and Wales said: ''It is not good to see anyone fall from public office but the decision by the Prime Minister to accept Andrew Mitchell's resignation seemed almost inevitable.

''Andrew Mitchell has apologised to our Metropolitan Police colleague and our colleague has accepted the apology.  We hope this matter is now closed.''

Labour's shadow Cabinet Office minister, Michael Dugher, said Mr Mitchell should have resigned earlier.

''After weeks in complete denial, Andrew Mitchell has finally bowed to public pressure. What people will want to know is why, when the entire country could see that what Andrew Mitchell did was wrong, the Prime Minister totally failed to act,'' he said.

''David Cameron is left looking profoundly weak and totally out of touch, doing everything he could to hold on to Andrew Mitchell only for his Chief Whip to bow to the inevitable, given the understandable public anger.

''There is a pattern of behaviour: an out of touch high handed Government where the Chief Whip can insult the police as plebs and the Chancellor thinks he has a right to sit in first class without paying the fare.

''This Tory Government day by day show they think it's one rule for them, another for everyone else.''

Nick de Bois, Conservative MP for Enfield North, said: ''Andrew has made the right call, but I feel a lot of sympathy, he's been through a very difficult time.

''I think he probably recognises that this had become a very toxic issue which was not allowing the Government to remain focused on its priorities.''