Voters go to the polls for a key by-election in British Prime Minister Gordon Brown's backyard on Thursday which will show if his leadership over the credit crunch can translate into an electoral renaissance.

Brown's Labour Party could count Glenrothes, a former coal mining area just north of Edinburgh, as a stronghold until recently but now faces a knife-edge battle with the Scottish National Party (SNP).

Glenrothes is the neighbouring constituency to Scotsman Brown's own in Kirkcaldy and Cowdenbeath and the premier has broken with convention by campaigning there in person, along with his wife Sarah.

If Labour wins, Brown can argue it shows support for his handling of the world economic crisis which saw him announce a bail-out for high street banks ahead of other countries, drawing international plaudits.

Labour has been behind in opinion polls since Brown pulled back from announcing a widely-expected general election in October last year but has regained some ground since the financial turmoil hit.

But if the SNP — which wants a referendum on Scotland splitting from England in 2010 — is victorious, leader First Minister Alex Salmond will claim it is a vote for independence, plus another victory against his old foe Brown.

Salmond and the SNP have enjoyed a honeymoon period since taking control of the devolved parliament in Edinburgh last year, announcing popular policies like a freeze in council tax, a tax on properties used to fund local authorities.

The by-election comes after the death of Labour lawmaker John MacDougall, who had a majority of over 10 000, in August.

Labour's recent record against the SNP in Scottish by-elections is poor — it was trounced by the nationalists at Glasgow East in July, surrendering its 25th safest seat in Britain and a majority of 13 500.

It has argued on the campaign trail that the economic situation highlights the case for a united Britain, saying the government bailout of Scottish-linked banks RBS and HBOS would have been impossible without the union.

Salmond, though, has accused Labour of "negative scaremongering" and has adopted US president-elect Barack Obama's slogan "yes we can" on the campaign trail to argue for independence.

Labour received a boost this week when crime writer Ian Rankin, who grew up in the constituency, backed "exceptional" Labour candidate Lindsay Roy, the head teacher at Brown's old local school.

SNP candidate Peter Grant is a local councillor who trained as an accountant.

Polls open at 7am (0700 GMT).

AFP