David Cameron warned yesterday that Britain was "running the risk" of having to revisit one of its darkest economic hours in the postwar period and borrow billions of pounds from the International Monetary Fund to keep the economy afloat.

In remarks that are likely to provoke Labour charges that he is running down the economy, the Tory leader spoke of a "frightening and worrying" scenario in which the nation's finances run dry.

"If we continue on Labour's path of fiscal irresponsibility, at some point - and it could be very soon - the money will run out," Cameron said in a speech to the Demos thinktank in London. "Then you will see the return of what happened under Labour in the 1970s, including emergency cuts to many of the public services on which a progressive society depends."

The Tory leader, who spoke of a "catastrophic fiscal position", said he was not setting a date by which Britain would turn to the IMF for emergency funds, as the former chancellor Denis Healey did in 1976 in a move which destroyed Labour's economic credibility and helped bring Margaret Thatcher to power three years later. But Cameron warned of a real and growing risk that Britain will have to turn to the Washington-based fund which usually helps developing nations.

"I am not saying that there is some date by which the government will have completely run out of money and we will end up back at the IMF," he said. "What I am saying is that we are running the risk of those things happening and those are risks that no government should responsibly run."

Labour will seize on Cameron's remarks to accuse him of talking down the economy. George Osborne, the shadow chancellor, was criticised for talking down the pound last year when he warned that Britain was heading for "a proper sterling collapse" if Labour continued to borrow at record levels.

Cameron raised the alarm over the IMF yesterday because he said that Britain would borrow next year at the same level as it did under Healey in 1976 - 8% of GDP. He fears this is likely to worsen because the 8% figure is based on a forecast of the British economy recovering this summer.

He said: "The frightening and worrying thing is that that forecast was made at the same time as [Alistair Darling and Gordon Brown] were standing up in the House of Commons and saying that the economy was going to start growing at the end of June this year. Now I hope that does happen. But a lot of people think it probably won't, in which case in the March budget there will be some pretty shocking debt figures and things will get worse."

Cameron's intervention came amid signs that Britain is being particularly badly hit by one of the most severe worldwide recessions in the postwar period.

Lord Turner, the head of the Financial Services Authority, raised doubts yesterday about the government's prediction of a recovery this year when he said the recession may last two years. "I do not know whether in three months' time or six months' time we are going to be able to use words like 'green shoots' without everybody thinking 'what an absurd thing to say'," Turner told Radio 4's Today programme. "But I do think that within two years say, we will clearly be on an up path."

The pound plunged to its lowest level against the dollar since 1985 on Wednesday, unemployment rose to a 10-year high of 6.1% in the three months to November and borrowing in the first nine months of the financial year doubled to its highest ever level of £71.2bn.

Mervyn King, the governor of the Bank of England, added to the sense of gloom on Tuesday when he warned that "unconventional measures" would be needed to kickstart the economy if interest rates reached 0%.