Downing Street has launched a fightback against criticism of David Cameron's handling of the Andrew Mitchell row, insisting the Prime Minister "stood behind" his cabinet colleague for as long as he could.

Mr Mitchell quit as chief whip in October after failing to quell a month-long storm provoked by claims he called police officers "plebs" in a foul-mouthed tirade.

He admits swearing during the spat but denies using the politically-charged insult and Scotland Yard is now investigating the possibility he was the victim of a conspiracy.

Allies of the senior MP told newspapers he was left "swinging in the wind" by the premier who they say failed to share CCTV footage from Downing Street that he had been told cast doubt on crucial accounts of the incident.

But Number 10 said Mr Mitchell had backed the Prime Minister's approach in the weeks after the initial story broke in The Sun, when he repeatedly called for a line to be drawn as Mr Mitchell had apologised to the officer concerned for swearing.

When the MP concluded the pressure had become too great, Mr Cameron accepted his resignation reluctantly, a spokesman said.

"The Prime Minister has deep sympathy for Andrew Mitchell after allegations emerged that a serving police officer fabricated evidence against him," Number 10 said.

"The Prime Minister stood behind his Chief Whip through weeks of growing demands to sack him. It was only when it became clear that he could no longer do his job that his resignation was accepted with reluctance.

"Andrew Mitchell did not disagree with the Prime Minister's approach throughout this period.

"The Prime Minister, and Andrew Mitchell, were deeply shocked to be informed that the police were investigating allegations that a serving police officer had lied about the events."