Gordon Brown insisted that he “always told the truth” last night as Labour and the Conservatives traded accusations of deceit in an increasingly personal row over public spending.

Answering David Cameron’s charge that there was a “thread of dishonesty” running through his leadership, Mr Brown said it was he who was being honest about action needed to boost the economy and rebalance the public finances in the long term.

“I have always told the truth,” the Prime Minister said in a BBC interview. “I have always told people as it is. I have explained we have a deficit reduction plan for the future. But you cannot do that without growth and employment in your economy.

“The honest thing to do is to say we have to get back to growth and jobs. The dishonest thing is to say this will happen without taking any action at all.”

Mr Brown, however, was forced to admit to a slip-up in an acrimonious Commons clash with Mr Cameron in which Mr Brown spoke of a “zero per cent rise” in spending in 2013-14.

He had meant to refer to a 0.7 per cent increase in current spending, but had failed to get the “seven” out. Mr Brown paid a heavy price for the omission as Mr Cameron and Tory MPs mercilessly ribbed him for talking about a zero per cent rise.

Mr Cameron had earlier opened up a new line of attack by suggesting that the Treasury’s own figures pointed to a fall in “total spending” after 2011, which the Conservatives insist to be the case if capital and current spending are combined.

Mr Brown first suggested that Mr Cameron was wrong and that total spending would rise but later made clear he was talking about current spending. He has now accepted the capital spending will fall before 2011.

The day of insults had begun with Lord Mandelson charging George Osborne, the Shadow Chancellor, with a “deliberate untruth” over claims that Mr Brown had refused the Tories access to key spending data.

Ministers were incensed by Mr Osborne’s claim in another BBC interview that Mr Brown had deliberately denied him access to figures he needed to draw up the Conservative spending plans.

Lord Mandelson fiercely denied the charge and challenged Mr Osborne to withdraw it.

“There is a very unattractive pattern of behaviour that is starting to emerge with George Osborne, of innuendo in pursuit of a smear,” Lord Mandelson said.

“Yesterday, George Osborne issued a very serious allegation that the Prime Minister had intervened to deny the opposition of information they were entitled to. This claim has been flatly denied by the Cabinet Secretary.”

The Prime Minister went close to suggesting that other departments might have to make cuts in order to protect the health, education and police budgets.

Mr Brown told the BBC that “there will be asset sales, there will be efficiency savings, there will be reforms in the way departments work” in order to bolster funding for frontline services.

Asked if there might be cuts, he replied: “I’ve got no interest... If these programmes are cut then that’s fine, but I’ve got no interest in keeping inefficient services that are not useful to society or the economy growing.

“But I want to get the resources to the front line, to policing, to hospitals and to schools.

“And you seem to be ignoring the main part of this debate - that you cannot do this without growth in your economy, you cannot do it without jobs in the economy. And the honest thing to tell people is you have got to take this action now, so that you can have growth and you can have jobs.”

He stressed investment now was crucial to returning the economy to growth and to reducing unemployment, itself vital to paying down debt on schedule.

The Liberal Democrats have accused the two main parties of staging a phoney debate about spending to prevent a proper discussion of the cuts that will inevitably be needed.

Nick Clegg, the party leader, accused Gordon Brown of “living in complete denial” about long-term savings which will be needed to balance the nation’s books and claimed Mr Cameron wants to cut spending now which would be “economic madness”.

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