The Glenrothes by-election will take place on Thursday, November 6, it was confirmed last night after a meeting of the parliamentary Labour Party at which it was declared that "hostilities are over" within the party.

George Howarth MP, who recently said Gordon Brown was as unpopular as Neville Chamberlain, told the meeting of MPs in the House of Commons that any rebellion against the Prime Minister was effectively over, signalling that, barring an accident, he will lead Labour into the General Election.

With a vote of confidence and a renewed sense of purpose in an economic crisis, Mr Brown announced to the meeting that the Glenrothes campaign would begin today.

The contest, caused by the death of the Labour MP John MacDougall in August, was widely expected to be held in the shadow of the US presidential election which would minimise any fallout if Labour loses the seat it is defending with a majority of 10,664.

Jim Murphy, the new Secretary of State for Scotland, is expected to be in the constituency today to launch the campaign with Labour's candidate, Lindsay Roy, a headmaster in Kirkcaldy.

Last night Mr Roy said that his campaigners were getting great support on the doorsteps. "The SNP run the council and the SNP run the Scottish government, and local people are angry at their cuts to schools, their higher charges for older people, and their plans for extra income tax," said Mr Roy.

The SNP candidate, Peter Grant, is favourite to win the seat and the SNP won the equivalent constituency in the Scottish Parliament last year. A series of opinion polls suggest the nationalists have a Scotland-wide lead over Labour in a UK General Election for the first time, but one poll put the parties neck and neck in Glenrothes.

John Mason, the newly elected SNP MP for Glasgow East, took his seat in the House of Commons yesterday, hours before the Glenrothes date was declared. Mr Mason won the Glasgow East by-election on 24 July, overturning a Labour majority of 13,507.

Mr Mason was watched by his family in the visitors gallery and cheered by his SNP colleagues as he was escorted to the Speaker's chair by Stewart Hosie MP, Dundee East and Peter Wishart MP, Perth and North Perthshire.

Speaking in advance of his swearing-in, Mr Mason said Glasgow East had sent him to Westminster with a message.

"It's clear and simple: it's time for action - action to help hard-pressed households who are struggling to make ends meet with the soaring cost of food and fuel," he said.

"During the by-election, SNP pressure forced a U-turn on the 2p rise in road fuel duty. People are struggling to make ends meet, and SNP success in Glenrothes will force more action over soaring household bills. The shame of fuel poverty in a land of energy plenty transcended the campaign in Glasgow East, just as it is now the defining issue on doorsteps in Glenrothes.

"The swing that elected me shows Labour's days of taking Scotland for granted are over. It is clear that people have had enough of Labour's broken promises."