Allies of Gordon Brown accused Darling of having made an "arse of it", after the Chancellor declared the economic times were "arguably the worst they've been in 60 years".

It came just days after Brown had declared that he believed the economic depression in Britain would be less severe than thought.

In an unusually candid interview, Darling also admitted that "people are pissed off" with the Labour Government, before declaring that Wendy Alexander, the former Scottish Labour leader, was "not likeable at all".

Darling later spoke to the BBC to deny he had denigrated Alexander. The Chancellor also insisted he had a duty to be straight with people.

However, First Minister Alex Salmond said Darling was guilty of talking the country into a recession, adding that he should "either step up to the plate or go now".

Bemused sources close to Brown said yesterday the Chancellor's interview may cause havoc with the Prime Minister's plans for a recovery package, which will begin this week with a major announcement on boosting the housing market.

"He's made a complete arse of it," said one senior Labour figure. "It doesn't help things when the Chancellor starts saying that the economy is down the tubes, especially when the Prime Minister just so happens to have been looking after it for the last 10 years."

There was also speculation last night that the interview may have put the Glenrothes by-election even further back in the calendar, to late November. In the interview, published in the Guardian, Darling said that the economic times faced by Britain and the rest of the world "are arguably the worst they've been in 60 years".

Emphasising the gloom, he added: "I think it's going to be more profound and long-lasting than people thought."

Darling said the Government had its "work cut out" to persuade the public it deserved another term in power. "This coming 12 months will be the most difficult 12 months the Labour Party has had in a generation, quite frankly," he said. "In 10 months we've gone from doing OK to certainly not doing OK. People are pissed off."

A Downing Street source said: "The Chancellor's words are the Chancellor's words."

On the BBC yesterday, Darling reiterated five times that the grave economic problems he was referring to were global in nature. His aides insisted he had not suggested the British economy was in its worst state for 60 years.

But Salmond said: "Scotland's economy is showing real resilience in what are challenging times, and Mr Darling's ridiculous interview is in danger of dragging everyone down to the Labour Party's own level."