The Conservative campaign has been criticised by two high-profile former ministers from the right and left of the party.

Kenneth Clarke, the former chancellor under Major who is known to be on the left of the party, has voiced doubts over the wisdom of attacking Tony Blair's personal integrity.

He also criticised the campaign's "presidential" style and said it was time to move onto other issues besides immigration.

Meanwhile, Norman Tebbit, a minister under Margaret Thatcher and godfather of the Tory right, said the party had not taken a strong enough line on immigration.

The Sun's editorial strongly criticises Michael Howard's tactics, saying: "The more he resorts to nasty name-calling and negativity, the more he emphasises the paucity of his own party’s policies and talent.

"Howard would not be allowed to call anyone a liar in the Commons, where there are strict rules on the use of un-parliamentary language.

"Doing so outside the chamber does not make him look hard. Just cheap."