MP Paul Marsden quit Labour yesterday to join the Liberal Democrats, saying he was "sick and tired" of the Government.

He disclosed he had been speculating about his widely-predicted move for "many months".

That was long before he clashed with Government Chief Whip Hilary Armstrong - North West Durham MP - over his opposition to the Afghanistan war and his claimed bust-up with fellow Labour MPs over his opposition to Labour's anti-terrorism Bill.

"I'm sick and tired of giving this Government the benefit of the doubt. Labour's let people down," said Mr Marsden, in a statement released by the Lib Dems at Westminster.

It is the first time a Labour MP has defected to the Lib Dems. The last time a Labour MP defected to its predecessor, the Liberal Party, was in 1974.

Mr Marsden had been involved in two highly-publicised clashes with the Government whips.

He first disclosed details of his conversation with Ms Armstrong over Afghanistan, and then complained he had been verbally and physical intimidated by "thugs" because of his opposition to the anti-terror legislation.

He had been summoned to see Ms Armstrong again yesterday, but it is understood the meeting never took place.

Instead, the Shrewsbury and Atcham MP's defection was announced by the Lib Dems.

He said in his statement: "Like more and more people in this country, I have lost confidence in the Labour Government.

"I have had enough of their obsession with control freakery and spin instead of policies which will really improve people's lives."

Labour insisted his defection was solely linked to his opposition to the war against terrorism.

Party chairman Charles Clarke said: "Before September 11, Paul Marsden had no central difficulty with Government policy, no difficulty with the whips, no arguments, no concerns."

But Mr Marsden's attitude changed after September 11, he added.

The 33-year-old MP, who came into the Commons in 1997, said later he had contemplated resigning and forcing a by-election in his constituency which he holds with a slender 3,579 majority.

"I understand the argument, but I was elected in June 2001 on four years of my constituency record as a Labour MP," he said.

Mr Marsden said he wanted to stand at the next election as a Liberal Democrat candidate in his constituency.

Lib Dems leader Charles Kennedy also welcomed defectors from the breakaway Pro-Euro Conservative Party - not members of the official party.

"Together, these new supporters from Labour and the Conservatives send a powerful signal.

"The Government is no longer trusted. The Conservatives are too extreme and the Liberal Democrats are now the party of the future in British politics."

The Lib Dems now have 53 MPs, the highest total of any third party since the Liberal Party, in 1929.

The Government's Commons working majority has now fallen to 164