Voting time: SNP candidate John Mason was an early bird at the polling station

A last minute  attack of nerves hit Labour today as the crucial Glasgow East by-election came to a nail-biting finish.

Late canvassing results suggested the result would be much closer than suggested by some headlines predicting a comfortable Labour victory, the Evening Standard has learned.

'There are a few hundred votes in it  -  and there is no guarantee that we win," said one insider.

Defeat in the Scottish heartland  -  regarded as the safest Labour seat in Britain  -  would be a huge blow to Gordon Brown's hopes of a quiet summer and would fuel speculation about his leadership in the run-up to the September party conference.

However, even a narrow victory would be celebrated by Labour activists as a sign that the Government is coming out of the doldrums and Mr Brown could enjoy a quiet summer while planning a big setpiece conference speech to spell out his future plans.

Labour cruised home in Glasgow East in 2005 with a massive 60.7 per cent of votes cast, beating the Scottish Nationalists by 18,775 to 5,268.

However, the 13,507 majority is threatened by a nationalist surge and lingering resentment over the 10p tax band abolition.

Labour was flooding the constituency with 400 extra activists to get the vote out today and candidate Margaret Curran declared: 'The Labour fightback is under way and we are on our way.'

But SNP First Minister Alex Salmond said the battle was 'neck and neck'.

Knife-edge: The by-election could be crucial for the political future of Gordon Brown

David Cairns, the Scottish Office Minister running Labour's campaign, admitted: 'It is going to be tight. It is too close to call.'

Some Labour insiders are furious that former Home Secretary John Reid, now chairman of Celtic FC, has not done enough on the stump to help Labour to win the by-election.

He clashed bitterly with Mr Brown when they were in Cabinet together.

Mr Brown will stamp his authority tomorrow regardless of the result by rejecting trade union demands for higher taxes and more worker power.

He will speak at the start of a policymaking forum in Warwick, where unions are making a show of strength.

It emerged that former Foreign Secretary Margaret Beckett could make a dramatic Cabinet come-back, to play a key role in presenting and explaining government policies in the media.

A seasoned performer, Mrs Beckett was widely admired for her skill and loyalty but was regarded as overpromoted at the Foreign Office.

She was dropped in Mr Brown's first reshuffle.

An insider said today that her recall was 'not unthinkable' although no decisions have been taken on a reshuffle.

Others in line for promotion include Jim Murphy, the Europe Minister, Caroline Flint, the Housing Minister, Liam Byrne, the Immigration Minister, and Health Minister Ben Bradshaw.

There was fresh speculation today that Mr Brown will hold his reshuffle in mid-September, presenting a team of fresh faces at the party conference.

Leading Blairites are to unite in a show of strength at the conference. Twelve big guns  -  including Peter Mandelson and Alan Milburn  -  are set to speak at a Progress rally on the opening night.

Jessica Asato, Progress's deputy director, said: 'This is not about personal attacks on Gordon Brown.

'This is about making sure that the party continues to articulate the concerns of the public with bold and progressive policies for the next decade.'