Labour must answer how it intends to fill a £10 billion black hole in its finances before the country goes to the polls in 48-hours, the Tories said on Tuesday.

Challenging Gordon Brown to say where he would find the money, Michael Portillo demanded to know which taxes would rise under a second-term Blair government.

"Labour must now say which stealth taxes they would impose to raise the £10 billion that they would need. People cannot be expected to go to the polls without knowing how much tax a Labour government would expect the to pay," he said at the Central Office press conference.

Portillo claimed that Labour would increase the tax on petrol - taking the price of petrol to over £6 a gallon.

"The tax on petrol has been Labour's favourite stealth tax. If Labour were to raise the £10 billion that they would need by increasing petrol tax, the price would have to rise to over £6 a gallon. If it's not to be petrol tax, then which taxes are Labour planning to increase," he said.

The Conservatives also claim that Gordon Brown is planning to scrap the ceiling on national insurance payments. Portillo claimed that removing the ceiling would result in those earning over £30,000 effectively paying a 50 per cent tax rate.

Interviewed on Monday, the prime minister refused to say whether Labour would scrap the ceiling on national insurance contributions. He told Newsnight: "What I can't do is sit here and write a budget."

Francis Maude told journalists that the election campaign was far from over. "It isn't over until the fat lady sings - and she hasn't even cleared her throat," he said.

In a surprise statement, Portillo gave a hint to the possible leadership fight that is yet to come.

Answering a question from a Mexican journalist, the shadow chancellor said that "people do get the government they deserve."

He then added words that will be seized on by both opponents and the media lobby. "If people are feeling apathetic then lets have better people stepping forward in the future."