Gordon Brown has come under intense pressure from Cabinet colleagues to break with prime ministerial convention and campaign in the crucial Glenrothes by-election.

Senior ministers said that while on paper another humiliating defeat for Labour was likely, a personal intervention by Mr Brown may save the seat, which neighbours his own.

Labour is still reeling from its catastrophic defeat in last month's by-election in Glasgow East and another may derail the Prime Minister's expected autumn fightback.

The party lost one of its stronghold seats to the SNP and many Labour MPs and party activists blamed the Prime Minister for absenting himself from the campaign.

“Gordon got the flak for Glasgow East even though he did not go there. He is going to get the flak for Glenrothes even though he goes and we lose. He might as well go,” a Cabinet minister told The Times.

Scottish MPs are also urging Mr Brown to lead from the front in Glenrothes and ignore the convention that prime ministers do not campaign in by-elections.

One MP said: “There's no question about it. He has to go and campaign this time because this is his home political territory. By going, he would lift morale. By not going, he would be sending a terrible message to Labour people on the ground that the seat isn't worth fighting for.”

The convention that Prime Ministers do not take part in by-election campaigns is more invented than formal and has been flouted only twice in recent years, both times by Tony Blair.

Mr Brown is believed to have taken a direct interest in Labour's choice of candidate for Glenrothes. The Times revealed yesterday that the frontrunner was Lindsay Roy, the head teacher of Kirkcaldy High, Mr Brown's former school. Mr Roy, who has been honoured for his services to Scottish education and is a friend of Mr Brown, would, local Labour sources said, make a formidable and articulate candidate.

Although Labour is defending a 10,600 majority, the SNP needs a swing of only 14.5 per cent, much less than the 22 per cent it achieved in Glasgow East.

David Cameron, the Conservative leader, has also confirmed that he intends to campaign and said that he hoped Mr Brown would “rise to the challenge of campaigning in his own backyard”. He said: “It is time for him to stop running scared and to stand up and be counted. I will be in Glenrothes. Will he?”

The Glenrothes by-election, which was caused by death of John MacDougall, is likely to take place at the end of October or beginning of November.

Mr Brown is due to begin his much-trailed fightback in the coming weeks,which will include economic help for hard-pressed families. His colleagues say that this could be derailed if he is seen to lose a third by-election in less than six months, following the abject defeats at Crewe & Nantwich and Glasgow East.

Losing Glenrothes would re-open the question of whether Mr Brown can lead Labour into a general election. There are strong signs that the senior MPs and ministers who plotted to oust him after Glasgow East have pulled back from making any further move against him for the moment.

Mr Brown is widely felt to have steadied the ship during the past few weeks and dissident ministers now believe there would be little attraction in a plot to oust him next month. They believe that the party would turn on them rather than Mr Brown if they handed the Tories such ammunition during the critical conference season.

They have let it be known that they will put pressure on him if the Glenrothes by-election ends in humiliation for Labour, another reason why the Prime Minister's allies say that he should throw caution to the wind.

Mr Brown's allies point out that he has a duty to Glenrothes's constituents as their neighbouring MP. “If he is going to the constituency to work, it is not a big jump to do a bit of campaigning,” one said.

Labour is due to select its candidate on Monday. Mr Roy, 58, a member of the local Labour party for the past 30 years, was appointed a CBE in 2004 and was appointed headmaster of Kirkcaldy High in May by the local SNP-controlled education authority after inspectors criticised the school for its poor exam results, disruptive pupil behaviour and low staff morale.

Mr Roy was a former headmaster of nearby Inverkeithing High, which, by contrast, regularly received glowing reports from the inspectors during his time as head.

The SNP has already chosen Peter Grant, the leader of Fife Council, as its candidate. The Liberal Democrats have appointed Harry Wills, and the Conservatives announced yesterday that Maurice Golden, an environmental campaigns manger, would represent the party.

Times Recommends

• A vicar’s wife: ‘There is no one to fight for us’
• Every little helps at the supermarket
• Ugg or Fitflop? The battle of the boots