The government has introduced a Fiscal Responsibility Bill in Parliament aimed at halving the deficit in four years - but Mr Cameron said Mr Brown's plan was to "put every decision off until after the election and say as little as possible between now and then".

Justice Secretary Jack Straw has accused the Tories of mounting "the most expensive election campaign in British political history" backed by "wealthy suitors".

Mr Cameron confirmed the party planned to spend £18m - the legal limit on election campaigning - but said the Central Office of Information, which he described as "the government's advertising arm", had a £500m budget.

"The government is spending vast amounts of money. They have got more spin doctors, more advisers, more press officers than they have ever had. So I think the money we are spending is responsible," he said.

On Saturday, Chancellor Alistair Darling warned that the next spending review would be the "toughest we have had for 20 years".

He said "many departments" would have budget cuts in in the next few years adding: "We are talking about something like a £57bn reduction in the deficit through tax increases and spending cuts."

Asked if he intended to reduce departmental budgets by more, or simply start cuts earlier, Mr Cameron replied: "It's both and one leads to the other."

A general election must be called by early June but commentators believe 6 May is the most likely date. Mr Darling also appeared to confirm on Saturday that there would be a budget before the election - saying he had one to do "in a couple of months".