Tory leader David Cameron conceded yesterday that Scotland could "stand alone" - but pledged to fight for the survival of the Union.

During a by-election campaign visit to Glenrothes in Fife, he promised to challenge any argument for independence.

Mr Cameron denied his party was wasting its time in Fife, despite polling fewer than 3000 votes in 2005, trailing Labour, the SNP and the LibDems.

Following the Prime Minister's refusal to campaign during the Glasgow East by- election, and his stated intention to visit Fife, Mr Cameron said: "I don't chop and change at by-elections. I turn up at all of them.

"I am here to help ensure the largest possible number of voters decide to vote Conservative."

The Tories' recent showings in the area did not deter his enthusiasm for fighting a campaign.

"I believe in campaigning vigorously wherever there is a Conservative standing," he said. "There is another choice in this election. The SNP thinks Scotland is better off on its own and Labour has let people down for 11 years. The Conservative Party will make a difference for people in Scotland by staying in the union.

"I think it is better for all of us to be in the United Kingdom. However, we wont solve it by frightening the Scots that they cannot make it on their own. I do not believe that. It won't win the argument. One of the first things I will do as Prime Minister is arrange to meet with the First Minister, whoever that may be, and work to further the benefits of the Union for people in Scotland."

During the day Mr Cameron met with some Scottish MSPs, including Scottish party leader Annabel Goldie.

He had a meeting with business leaders from the Fife Chamber of Commerce and some local estate agents to discuss the current problems they face. Later in the day he joined the candidate Maurice Golden, in knocking on doors urging people to vote Conservative.

Following Wednesday's stage-managed Sarah Brown visit, there was to be no media presence on Mr Cameron's canvassing operation.

A party spokesman said: "It is to allow Mr Cameron to be able to speak to people privately, as in a normal campaign day."

Mr Cameron said not to expect his wife Samantha on the streets of Glenrothes.

"My wife works four days a week, today is a working day, she is not planning to come. She does occasionally do some light canvassing for me personally in Oxfordshire at election times," he said.

A jovial side of the Conservative leader was shown when asked if he would take on Alex Salmond, paraphrasing boxing great Muhammed Ali.

On Wednesday, Mr Salmond challenged Gordon Brown to come to Glenrothes and debate with him "toe to toe".

When asked if he would be prepared to "go toe to toe" with the Prime Minister he replied: "I am not sure what he means by toe to toe, is he taking about ballet or boxing?

" I will dance like a butterfly sting like a bee."

Labour sought to woo the pensioners of Glenrothes with the visit of James Purnell to the constituency. The Work and Pensions Secretary criticised the Tories' record on helping the elderly.

He said: "David Cameron's visit to Scotland just highlights the stark difference between Labour and the Tories. The Tory government abandoned pensioners in the last economic downturn and was happy to use unemployment as an economic tool.

"We are helping pensioners, and helping people get back to work."

Mr Purnell highlighted the looming rise in the winter fuel allowance to £250 for pensioner households.

"Labour introduced the winter fuel payment in winter 1997 to make sure people like the pensioners I met today can stay warm in the winter," he said.

"The £50 extra this winter will help cover the increased costs of fuel. It's vital that we help pensioners this winter, and that's why Labour's decision to give free insulation to all pensioners aged over 65 is so important."

SNP candidate Peter Grant highlighted free bus travel for the elderly and called on Westminster to bring in a fuel duty regulator to stabilise petrol prices.

"More and more people are using the bus as an alternative to paying high petrol prices," he said. "While the SNP is expanding free travel services, Labour are looking to increase taxes on those who have to drive.

"Instead of helping ease the burden of bills as the SNP is doing, Labour look set to pile the pressure onto Fife families."

Mr Grant continued: "The SNP is the only party that has put forward serious proposals to bring fuel taxes under control with a fuel duty regulator - a policy all other parties failed to support.

"In Glasgow East the prospect of an SNP win brought a freeze on fuel duty. In Glenrothes an SNP victory will help keep fuel duty down."

The Liberal Democrat campaign took former party leader Charles Kennedy to a bagpipe manufacturer, JT Shepherd and Son, in Cardenden. "The SNP are full of hot air and Labour have run out of puff," said candidate Harry Wills.

Mr Kennedy said: " "I'm very pleased to be joining Harry today, with just two weeks left until the people of Glenrothes choose their new MP.

"It is increasingly clear they face a choice between an MP, in Harry, who will fight for Fife, and an MP who is more concerned with the petty squabbling of Labour and the SNP."