Tony Blair today warned Labour not to repeat the mistakes of the 1980s which consigned the party to years of opposition.
In a rare intervention, the former prime minister said that for the party to shift to the left in the wake of their general election defeat would be to treat the electorate as if they were stupid.
His comments, to the centre left Progress think-tank, came as the first public opinion poll in the Labour leadership contest put Jeremy Corbyn on course for a shock victory.
Mr Blair said that the left winger was the "Tory preference" and he urged supporters to engage "very strongly" in challenge he represented.
"After the 1979 election the Labour Party persuaded itself of something absolutely extraordinary," he said.
"Jim Callaghan had been prime minister and the Labour Party was put out of power by Margaret Thatcher and the Labour Party persuaded itself that the reason why the country had voted for Margaret Thatcher was because they wanted a really left wing Labour Party.
"This is what I call the theory that the electorate is stupid, that somehow they haven't noticed that Margaret Thatcher was somewhat to the right of Jim Callaghan."