Calling Stephen Harper the "King of Deficits," former prime minister Paul Martin laced in to the Conservative record on the economy — and accused the NDP of "holding hands" with the Tories on the path to fiscal ruin.

"The current Conservative government has ground the economy down so far, trampling the most vulnerable of our citizens in the process, that the next government has to act," Martin said in a hard-hitting speech at a Liberal campaign event in Montreal on Friday. "And that the NDP doesn't understand that, boggles the mind."

Martin said the NDP's promise to balance the books immediately would be bad for the economy, and accused leader Tom Mulcair of taking lessons from the Conservatives.

"That Tom Mulcair is now a student of Stephen Harper's economy makes no sense," he said.

Is Trudeau now 'candidate of the left'?

Liberal Leader Justin Trudeau is beating back criticism for his plan to run three consecutive "modest" deficits and spend $125 billion on infrastructure over the next decade to stimulate the economy.

Asked if he's comfortable being framed as the "candidate of the left" in the campaign, Trudeau insisted he is only being transparent.

"I'm the candidate who's actually telling the truth to Canadians," he said. "I've made a choice to be open and honest about our economic situation. We are currently in Mr. Harper's eighth straight deficit."

At a campaign rally in Montreal, Mulcair shot back and called Martin the "king of austerity."

"They [Harper and Trudeau] both want to live for today and let tomorrow take care of itself," he said.

"There's a reason we want to be good public administrators with balanced budgets, because if we're not then we're not going to be able to have the types of programs that we all believe in going in to the future."

The war of words came just as the federal government announced a $5 billion surplus for the first three months of the fiscal year. In its monthly Fiscal Monitor report, the Department of Finance revealed that government revenues came in at $24.3 billion in June, a surplus of $1.1 billion.

The sale of the government's remaining stake in General Motors accounts for about $2.1 billion of that $5 billion surplus.

More Duffy trial questions

And Trudeau also reacted to a report that Harper's chief of staff, Ray Novak, told CTV News that he did not know about the $90,000 cheque Nigel Wright wrote to cover Senator Mike Duffy's expenses.

"Canadians aren't fools. They know that the prime minister and his senior staff have not been telling them the truth. The prime minister is known for his controlling approach to everything that goes on in his office," he said.

"The fact that his closest adviser pretends that he wouldn't have read emails or wasn't paying attention during crucial meetings like that simply insults the intelligence and credulity of Canadians."

Mulcair said he has no quarrel with subordinates in Harper's office, but urged the Conservative leader to "start coming clean with Canadians."