The voters of Glasgow East go to the polls tomorrow for a by-election contest that will determine whether Gordon Brown can enjoy the early days of his summer holiday.

The main parties today made their final push in the seat, where Labour is defending a majority of 13,507 but would settle for that falling to 100 tomorrow. A win is a win and one vote really would be enough.

In the party at Westminster there is a quiet and cautious confidence that Labour’s Margaret Curran can win the day. Despite the hype, when the seat became vacant this by-election was never going to decide the fate of Mr Brown - and that remains the case, even if the SNP turn the tables tomorrow.

The pundits who equated Mr Brown’s future with the result in Glasgow ignored the fact that the contest had been deliberately timed to happen after the Commons had risen for the summer recess and when many of the key players - Mr Brown included - would be packing their bags for the beach.

But that does not mean it is not absolutely key to Labour’s and Mr Brown’s mood as they contemplate the next few months.

A Labour win tomorrow would undoubtedly take the pressure off the Prime Minister, allow him a proper holiday (he has arranged a rota of Alistair Darling, Jack Straw and Harriet Harman to cover for him while he is away), have a think about a reshuffle in September and plan a strategy to avoid a new crisis over his leadership developing during the conference season.

But an SNP win would send Labour MPs away in a churlish state, making them wonder even more whether the party can recover under Mr Brown.

Mr Brown’s next big hurdle will be the Labour conference. He needs to win in Glasgow and a change of political fortune, however slight, to convince his party that it should stay with him and rely on him to turn things round. Potential successors are hardly impatiently knocking on the door. It is not a good time to have another leadership election. Even if there was one, the victor would have to call a general election swiftly. Two unelected prime ministers in one Parliament would be more than the voters could take.

Mr Brown’s biggest obstacle probably remains next year’s local elections in May. A repeat of this year’s debacle, just one year out from a general election, might start MPs panicking again, and anything could happen.

But that is a long way off. Today, as he writes his speech for Labour’s policy forum meeting in Warwick on Friday, Mr Brown will be hoping that his team in Glasgow - aiming to knock on 10,000 doors today - are successful.

Most observers of the by-election are predicting a fairly narrow Labour win and that is what the bookmakers forecast as well. But as usual, factors like the weather could play a big part tomorrow.

Labour have sought to focus the campaign on Ms Curran. Ministerial visits have been low-key and Mr Brown, in line with custom for PMs, has stayed away.

In a TV debate last night Ms Curran said she would vote against the Labour government if she judged it necessary.

“If it were required, and I was absolutely having to do that, I would”, she said on STV’s Politics Now by-election special Today.

“Voters tomorrow have a very clear choice to make over what kind of MP they want. By backing me they will be electing someone who will stand up for the east end and never, ever, talk it down.

“If they support my opponent, the self-confessed hard-line nationalist councillor Mason, they will be electing an MP who is obsessed with breaking up the UK and can see no difference between Labour and the Tories.”

The SNP’s final day of campaigning included a visit to a bowling club by Nicola Sturgeon, the deputy First Minister, and comedienne Elaine C Smith with candidate John Mason, a Glasgow councillor.

Alex Salmond, the First Minister, who has been campaigning in the constituency almost every day, has raised the stakes by declaring the contest to be a “test of strength” between his government and Gordon Brown’s.

“People are passing judgment clearly on a Labour Government at Westminster but clearly they are also passing judgment on the SNP Government in Scotland,” he said yesterday.

Liberal Democrat Ian Robertson will concentrate on his campaign to save Parkhead fire station. He will be joined by Holyrood politician Ross Finnie and MEP Elspeth Attwooll as they hand a petition to Glasgow City Council.

Tory candidate Davena Rankin will round off the campaign with Annabel Goldie, Scottish Conservative leader.

Solidarity billed its last day on the campaign trail as the only true public event. Candidate Tricia McLeish will be with activists at a public meeting in Easterhouse.

SSP candidate Frances Curran will play up the differences with her Labour counterpart by unveiling a Curran versus Curran poster.

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