A Labour MP complained to Tony Blair that he had been physically and verbally assaulted by "thugs" in the party's whips office.
Paul Marsden, the MP for Shrewsbury and Atcham, claimed he was manhandled and repeatedly abused by his own colleagues after criticising the Government over its controversial Anti-terrorism Bill.
The allegations were fiercely denied by Labour whips, who claimed the MP was attempting to provoke a row that would end in his defection to the Liberal Democrats.
In a strongly worded press release, Mr Marsden said several whips intimidated and insulted him as they left the Commons chamber in the early hours yesterday.
He accused one whip, Jim Dowd, of prodding him in the back and another, Gerry Sutcliffe, of telling him he could not prevent other Labour MPs from physically attacking him.
Later, he claimed the ugly scenes spilt over into a Commons bar where Mr Sutcliffe put his arm across Mr Marsden's throat and several Labour MPs shouted abuse at him. Mr Marsden said: "I have witnessed the crudest attempts yet to silence me. In a country that prides itself on freedom of speech, members of Parliament can be subjected to the worst kind of bully-boy tactics."
In a letter to the Prime Minister, he said: "If no action is taken in investigating this, I take it you endorse physical and verbal threats to Labour backbenchers. It is yet another sad day for democracy and a clear indication that your thugs hold Parliament in contempt."
His version of events was strongly disputed by Labour whips , who denied any physical assault had happened. One source condemned his allegations as "increasingly erratic" and insisted that only "robust conversations" had taken place with Mr Marsden.
However, senior Labour sources admitted patience had run out with the MP. They suspect he is planning to defect to the Liberal Democrats, an accusation he denies.
One source said: "We are not going to take any action against him. We are certainly not going to help him in his ambition to become a martyr."
The claim and counter-claim marks a new low in the stormy relationship between Mr Marsden and the Labour hierarchy.
He enraged party chiefs in October by revealing details of a confrontation with the Chief Whip, Hilary Armstrong, after he denounced the military action in Afghanistan. She allegedly compared him to the pre-Second World War appeasers of Nazi Germany and told him: "War is not a matter of conscience".
In the Commons last night, Gerald Howarth, the Tory MP for Aldershot, called for action "to protect dissident members of the Government from physical attack and intimidation from their own whips".Reuse content