Labour hold a 10,664 majority in the seat, but the SNP have been installed as the bookies’ favourites following their success at the Glasgow East by-election in July, where they produced a massive swing to overhaul an even bigger Labour lead on that occasion.

Labour’s Lindsay Roy, headteacher of Gordon Brown’s former school, voted at Collydean Primary, accompanied by his wife Irene, as did SNP candidate, Fife Council leader Peter Grant, and his wife Fiona.

Both hopefuls have fought a long and wide-ranging campaign, with Labour hoping visits from Prime Minister Gordon Brown and his wife Sarah, Chancellor Alistair Darling and, yesterday, former Deputy Prime Minister John Prescott have helped to win crucial votes.

Mr Prescott said, “Nationalism is not the answer — Salmond can’t do anything about the global problems we’ve got at the moment. All his international arguments have gone.”

Mr Grant, meanwhile, has been supported by around a dozen visits from First Minister Alex Salmond, while cabinet ministers Nicola Sturgeon, John Swinney and Shona Robison have also been prominent on the campaign trail.

Mr Salmond insisted his party can win the by-election, urging people to choose his party’s “positive record” over the “negativity” of Labour.

“In a week when the world is looking forward, it is clear the SNP can win the Glenrothes by-election,” he said.

“Just as Americans voted for hope over fear, people in Glenrothes can choose between the positive record of the SNP and the negativity and scaremongering of Labour.

“We have been to every corner of the constituency, up every street and on every doorstep.

“By far the most powerful election leaflets in this campaign have been the massive gas and electricity bills thudding though letterboxes and reminding people that Labour have done nothing to help.”

The battle for third spot is also said to be too close to call, with the Conservatives hoping to edge out the Liberal Democrats.

Conservative Maurice Golden welcomed Scottish Tory leader Annabel Goldie to town yesterday and added, “Every vote for the Conservatives is another voice in the growing chorus for change sweeping across Britain.”

Lib Dem candidate Harry Wills, backed by Willie Rennie MP, a winner over Labour in Dunfermline and West Fife in 2006, believes his party is sending out a message voters can relate to.

“Labour and the SNP will put Gordon Brown and Alex Salmond first, but for me, the residents of Fife and Glenrothes will always come first,” Mr Wills said.

Voting closes at 10pm, with the result expected in the early hours of tomorrow morning.