George Osborne has been urged to "stay the course" by a leading forecaster as he faces intense pressure after shock figures revealed the extent of the recession biting Britain.
The chief of the Organisation for Economic Co-Operation and Development warned that any relaxation of the Government's economic position would be punished by the markets and ratings agencies.
OECD secretary general Angel Gurria insisted that austerity measures now were "sowing the seeds of what will be the elements for recovery".
Dismissing speculation the double-dip recession is putting Britain's coveted AAA credit rating at risk, he said: "I don't think that's the case. References to that were not made by rating agencies."
"I think what the rating agencies are looking for is consistency and coherence and that today is at a very big premium. They are the first ones who will turn on you if they see you are not performing."
His comments fly in the face of warnings by analysts that the figures, which revealed GDP shrank by 0.7% between April and June, could lead to a downgrade.
Alan Wilde from Baring Asset Management told the Financial Times: "No amount of excuses about rainfall or the Queen's Jubilee can explain away such weak growth.
"Osborne's personal ratings for economic competency are plummeting and the credit rating agencies will be deeply concerned... This may well hasten a downgrade."
Losing the AAA, which the UK has held since 1978, would make it more expensive for the country to borrow and would further jeopardise the coalition's economic plans.
Ratings agencies have not so far commented on the new data but Moody's gave the UK a 30% chance of losing its rating within 18 months back in February.
Since then, the eurozone crisis has deepened, UK borrowing has risen and the recession here in Britain has officially become the longest-double dip since records began in 1955.
After the latest growth figures, Mr Osborne admitted Britain had "deep-rooted economic problems" but gave no indication of a change in economic strategy.
Mr Gurria, speaking on the BBC 4 Today programme, urged Britons to show patience with the schemes already announced by the coalition and warned against further spending as a knee-jerk reaction.
Asked what advice he would give, he said: "Stay the course, I would say to the Chancellor that the cost of wavering or looking like you are wavering or looking like you are weakening your resolve today because of what is happening in the markets - because of Spain and Italy and Greece and everything else - is very high indeed.
"Perhaps the flexibility that under normal circumstances one could show - a little bit of weakening and maybe extending the periods for the goals and things like that - today could be misunderstood.
"I think we have to give very strong signals here, and the Chancellor, the Prime Minister and the Deputy Prime Minister are all really quite intent in staying on course and staying on message.
"This is very important, this is why the UK adjustment programme cleared the markets, this is why you have very low borrowing costs, this is why I think you should persevere.
"You are now sowing the seeds of what will be the elements for recovery. You have to have credible public finances before you start moving on growth."
However, former Lib Dem Treasury minister Lord Oakeshott has called for Mr Osborne to be ejected and replaced by Business Secretary Vince Cable in the September reshuffle.
"George Osborne has got no business experience. He has never worked outside politics. He is doing surprisingly well for a chancellor on work experience but really in a torrid time like this I think we do need absolutely the best people available," the outspoken peer said.
Mr Cable, who is a personal friend of Lord Oakeshott, dismissed the remarks as the words of an "independent political and economic commentator with strong views of his own".
"I don't happen to agree. We have a very good team in the Government and the Treasury and I work very harmoniously with them," he said.
Pushed later on BBC's Newsnight about whether he wanted the job, Mr Cable said he would "probably" make a good chancellor but stressed that he was not calling for a change.
"George Osborne is doing the job, we're doing it together, well, as part of a team, and nobody's suggesting we change the arrangements," he said.
