With a poll yesterday showing that Labour can only win a clear victory in the next General Election if Tony Blair steps down in favour of Chancellor Gordon Brown, trust in the Prime Minister appears lower than ever.

Two years ago when Mr Blair celebrated his fifth year in office it seemed that no political crisis could stick to the politician known as Teflon Tony.

The economy has looked rosy with interest rates at their lowest point since the 1960s and unemployment at levels last seen in the early 1970s.

And for the first five years Mr Blair performed a feat never previously seen, giving Labour a comfortable lead in the opinion polls every month since coming to power except one.

But bruising internal party battles over university fees and foundation hospitals, the decision to go to war in Iraq, the failure to find Saddam Hussein's weapons of mass destruction, the David Kelly affair and now the torture allegations have severely dented Mr Blair's standing with voters.

Yesterday's YouGov poll in the Mail on Sunday indicated Labour would win the next election but fall short of a Commons majority with Mr Blair in charge. But it would win a majority of 77 seats if he handed over to the Chancellor.

Former Foreign Secretary Robin Cook said yesterday the time would come when Mr Blair had to ask himself if he should quit because the "major mistake" of Iraq was overshadowing his domestic achievements.

Mr Cook said Mr Blair had been the most successful Labour leader of his lifetime.

But he added: "I think Tony Blair, in a way now, is a victim of a tragedy in he has had a tremendous record of achievements on the domestic front.

"The trouble is none of it is now getting any attention because of, what I believe was a major mistake, of going into Iraq without international support and without any clear idea of what we would do after the war was over."

Earlier, a Labour peer and personal friend of Mr Blair urged him to resign and hand over to Mr Brown.

Film-maker Sir David Puttnam said the Premier was now synonymous with the "bad news" flowing out of Iraq.

Sir David said months of negative headlines about Iraq would damage Labour's electoral prospects and Mr Blair should resign before this summer's Commons recess.

He said the Chancellor would inevitably be the man to take over.

Sir David is the latest in a growing number of Labour figures calling on Mr Blair to go. Former Chancellor Lord (Denis) Healey this week called on Mr Blair to resign before the next General Election.