Labour leader Ed Miliband tried to turn the way Britain’s two largest political parties are typically seen on its head on Monday, claiming his was fiscally responsible whereas the Conservatives were “throwing promises around” with no idea how to pay for them.

Miliband was speaking in Manchester where he unveiled the Labour Party’s manifesto for the May election. He insisted the plan did not contain a single policy that wasn’t “paid for without a single penny of extra borrowing.”

Prime Minister David Cameron’s party, by contrast, has promised to spend £8 billion more on the National Health Service and cut taxes by another £8 billion in the next parliament — without specifying where the money would come from.

“You can’t fund the NHS with an IOU,” Miliband said. “Every promise we make is paid for. That is the difference between the Conservative Party and the Labour Party.”

Coming from a party that has spent five years in opposition criticizing austerity and calling for higher public spending to stimulate an economy that is now growing faster than most in the developed world in spite of Labour’s claims that Tory cuts would nip the recovery in the bud, the rhetoric is ironic to say the least.

Or, as the BBC’s Robert Peston puts it, “Labour has subjected itself to discipline which the Tories have decided they don’t need (largely because they think voters will give them the benefit of the doubt, based on the cuts they’ve delivered in the current parliament).”

Miliband vowed that under Labour, “The deficit will be cut every year. The books will be balanced and the national debt will be falling.” But that commitment is far less ironclad that it sounds.

Peston notes that if economic growth keeps up, the deficit will fall relative to gross domestic product anyway. Labour would probably even be able to spend up to around £40 billion more than the Conservatives plan to between the election and 2020 and still meet its promise of cutting the deficit every year.

The party could also make good on its promise to balance the books by the end of the next parliament without making additional spending cuts at all.

The Conservatives and Liberal Democrats, by contrast, who currently rule in coalition, want to eliminate the deficit by 2017-2018.

The two parties inherited a £149 billion shortfall from Labour in 2010, then equivalent to 11 percent of GDP. They cut it in half to £76 billion this year, or 4 percent of GDP.

Miliband is right when he accuses the Conservatives of making unfunded spending promises. But Peston is also correct when he notes that they — unlike Labour — are credible. Miliband’s conversion to fiscal discipline comes late in the game. Too late, perhaps, to convince voters Labour is serious this time.

The socialist party’s manifesto still contains plenty of goodies, from cutting university fees by a third to freezing rail fares as well as utility bills to raising the minimum wage. The party would bring back the 50 percent tax on annual incomes over £150,000 to help pay for some of the measures although the abolition of the highest tax rate under the Conservatives actually saw revenue from top earners increase. A higher marginal rate might not actually bring in more revenue as those subject to it find ways to circumvent the tax.

Labour would also introduce a property tax for homes valued at £2 million or more to finance an extra £2.5 billion in annual spending for the National Health Service.