With a week of campaigning to go in Fife, Labour began to draw level in the odds with the SNP on the day when the latest efforts of the Prime Minister's wife were kept under wraps.

Sarah Brown was used as a stealth weapon again yesterday, campaigning unannounced in the main shopping centre in Glenrothes.

Stealth campaigning was not what shoppers in the Kingdom Centre faced for the rest of the day, with all the main parties spending time in what is effectively the constituency's Main Street and where the operators are now allowing strictly-controlled campaigning.

The bookmakers are making it an increasingly close contest. William Hill said yesterday that they had not taken any bets on the SNP winning the seat since Prime Minister Gordon Brown campaigned there at the weekend. The bookmakers have the SNP as narrow favourites, with Labour rapidly closing the gap.

William Hill spokesman Rupert Adams said: "Since Gordon Brown went up to Glenrothes we have not taken a penny on the SNP and a Labour victory now looks on the cards."

As BP posted its biggest quarterly profit of £6.4bn, SNP candidate Peter Grant urged the UK Government to use the tax revenue it receives from oil companies to help families pay for fuel this winter. He said: "With BP making over £800 a second in profits from rising oil prices the UK Government will be raking in extra money in taxes that could go towards supporting Fife families through this winter."

Deputy First Minister Nicola Sturgeon joined Mr Grant, shopping in a local supermarket, and saying: "The Scottish Government has taken practical steps to put more money back into people's pockets and purses. With energy bills continuing to rise and no action from Gordon Brown to deliver lower bills this winter, balancing the family budget is becoming harder and harder."

Labour candidate Lindsay Roy was campaigning with UK Veterans Minister Kevan Jones. They met Fife veteran James Lewis and Mr Jones said: "We owe all our Armed Forces a tremendous debt of gratitude for all that they have done - whether that is from many years ago or this year.

"They are a credit to our county and Mr Lewis is a credit to Fife."

Shadow Defence Secretary Liam Fox was also in Fife, visiting a the war memorial in Markinch with Tory candidate Maurice Golden. Mr Fox said: "Every place in Britain has some memorial to those people who have sacrificed so much for our safety and security.

"There can be no better time than a by-election to remind people that the political freedoms we have come at a very high price."

Mr Golden said: "We may be in the midst of tough economic times but it is right that we pause to remember those who have given service to our nation, and those who are serving on the front line today."

Liberal Democrat candidate Harry Wills backed Fife miners campaigning to get compensation for a debilitating condition known as "miners' knee". Those with the condition can experience severe pain in the knee joint and swelling, with many finding it difficult to walk without assistance.

Mr Wills said it was "entirely right" that miners with the condition should receive compensation.