The Labour Party will lose the general election if Tony Blair remains leader, the Conservative co-chairman has claimed.

Party chief Lord Saatchi said on Tuesday that the prime minister is an "irrecoverable" liability for Labour, according to Tory polling.

He said the two-times election winner is a "messianic man with stars in his eyes looking at the promised land in the distance".

Despite surveys showing that the government is still on track for re-election next year, the opposition argued that the public's loss of faith in Blair will cost his party crucial seats.

Private polls suggest the Tories are ahead in 103 of their 130 target constituencies, enough to deprive the prime minister of his Commons majority.

While the Conservatives would not win outright on the basis of these figures, the chairman and election chief said they showed the progress that had been made by Michael Howard.

"If Tony Blair is still the prime minister, I can't see any way in which Labour can win the general election," Lord Saatchi told the BBC.

"According to our own figures, we already will win enough of our target seats for Labour to lose power.

"That's why I say I can't see how they can win because the position they have got themselves into in terms of disillusionment - he in particular - is irrecoverable."

The former advertising executive is an expert on public opinion but some may see his comments as designed to dismiss Tory doubts about their chances of success, rather than destabilise Blair.

The prime minister has made clear he would step down as Labour leader if he felt he had become a liability to the party, but despite his problems with trust and Iraq, most Conservatives still fear his ability to win over swing voters by capturing the centre ground of politics.