Tebbit claims Cameron is losing Tories' traditional supporters

Lord Tebbit has launched the strongest Tory attack on David Cameron since he became the party's leader, warning that he risks alienating its natural supporters.

Writing in The Spectator magazine, the former Tory chairman accused Mr Cameron of ignoring up to five million voters who have deserted the Tories by chasing Labour and Liberal Democrat supporters.

He warned the Tories could miss a good electoral opportunity. "The strategy seems to be aimed at persuading Liberal and Labour voters that the Cameron party shares their beliefs and aspirations and would deliver Blairism where Blair has failed," he said.

Lord Tebbit argued that last month's by-elections in Bromley and Chislehurst, where the Tories squeaked home, and Blaenau Gwent, were a " humiliation" for both the Tories and Labour.

"The present Conservative strategy is eroding its ultra-loyalist bedrock vote," he wrote. "Modern Conservatives give the impression that respectable working- and lower-middle-class supporters in the suburbs, country towns and villages are not quite good enough for the new 'A' list, Notting Hill party."

He claimed that the Tories were clutching favourable opinion polls " like a baby grasps for a dummy". But as many voters were backing " none of the above", the Tories could not tell whether Mr Cameron was gaining new supporters or if his lead was due solely to a haemorrhage of support for Labour.

Lord Tebbit warned the Tories not to underestimate Gordon Brown. "It is hard to believe that in an election soon after becoming Prime Minister, Gordon Brown would be less popular than Tony Blair," he said. "His undeserved reputation for conservative economic policies, his lack of personal avarice and his support for sterling and family life would reassure moderate opinion and allow him to woo back Labour's lost voters with leftist mood music."

The attack came as Labour launched an offensive to end Mr Cameron's political honeymoon. Douglas Alexander, the Transport Secretary, said the Tory leader was "doomed to fail" as he had not secured the fundamental change achieved by Labour before it regained power in 1997.

He said in a speech in London: "You can change the sales strategy. You can change the branding and the packaging. But fundamentally the Tories have to change the product."

* Support for the Tories has reached a 13-year-high of 39 per cent, according to a Guardian/ICM poll. The Liberal Democrats dropped to 17 per cent, their lowest level for four years, while Labour were up three points to 35 per cent.