MP's death leaves Brown facing fresh Scottish by-election nightmare as Miliband reignites leadership row

The former oil rig worker, who died of cancer at the age of 60, had a majority of 10,000 in Glenrothes, Fife  -  next door to Mr Brown's own constituency.

With the Scottish Nationalists overturning a 13,500 Labour majority in Glasgow East last month, the once-safe seat looks highly vulnerable.

Poll: John MacDougall's death leaves Gordon Brown facing another by-election

There was more bad news for the Prime Minister when Foreign Secretary David Miliband repeated his call for a new 'vision' for Labour, which was widely seen as a leadership bid.

Last night a poll gave the SNP a 13-point lead over Labour, the biggest ever recorded and enough to oust Chancellor Alistair Darling, Defence Secretary Des Browne and a string of other Scottish Labour MPs.

The Glenrothes by-election is unlikely to be held before late October or early November.

Defeat there would wreck a planned Brown 'relaunch' at next month's party conference and could provide a focal point for MPs seeking to oust him.

Unrepentant: Foreign Secretary David Milliband refused to apologise for setting out his 'vision' again yesterday

Mr Miliband insisted yesterday that he had no regrets about setting out a personal manifesto for beating the Tories which made no mention of Mr Brown.

Asked if he had had second thoughts, the Foreign Secretary replied: 'No. I think the article set out a very clear agenda for defending the record of the Government, for advancing a clear vision of the future, of Britain's new place economically, socially and internationally  -  and for drawing a strong contrast with the Tories.'

He was careful to praise Mr Brown's 'determination and vigour', but then said cryptically that being Foreign Secretary was his job 'at the moment'.

There was more embarrassment for the Prime Minister when a Government aide intervened on live radio to try to stop a minister being questioned about his chances of survival.

Work and Pensions Minister James Plaskitt was asked on BBC Radio 4's The World at One whether the worsening economic prospects would further destabilise Mr Brown.

He replied: 'I am not commenting on that issue, as I made clear at the outset. It is not about that.'

A woman Press officer, sitting in on the interview, was then heard to tell the presenter: 'We are only talking about today's unemployment figures.' Asked again whether Mr Brown's leadership would be affected, Mr Plaskitt replied: 'The answer's no.'

Former Deputy Prime Minister John Prescott warned yesterday that Labour is too obsessed with internal battles rather than running the country and has lost the trust of those people who are calling for change.

'We need to remind people what we stand for and then put the Tories on a bit of a run,' he said. But he insisted Mr Brown is the best person to take Britain through economic turmoil.

The Prime Minister paid generous tribute to Mr MacDougall, who was diagnosed with the asbestos-related cancer mesothelioma more than two years ago.

Mr Brown, who had visited him on Monday, said he was mourning the loss of a 'good personal friend' and a 'true servant of the people'.

The Prime Minister avoided taking part personally in the ill-fated Glasgow East campaign, but will find it almost impossible to avoid one in Glenrothes.

The seat covers part of Kirkcaldy, the town he also represents. He is likely to visit his constituency office several times during the campaign, and would be criticised for refusing to take part in a knife-edge battle a few hundred yards away.

One senior Labour figure said: 'Gordon got the s*** kicked out of him after Glasgow East. He has to show we're in this one to win. Defeatism and defensiveness is not the message to give off.'

The last by-election in Fife, in February 2006, saw the Liberal Democrats seize Dunfermline and West Fife from Labour.