Former chairman and deputy leader Michael Ancram urged Mr Cameron to unveil the party's "soul" by returning to core values on issues like tax, Europe and marriage.

In a 30-page document that amounts to an alternative traditionalist manifesto, Mr Ancram denounced efforts to present the Conservatives as the "heir to Blair", and insisted they should instead embrace Thatcherite achievements.

While he applauded some of his leader's policies and the proposals emerging from policy review groups, the intervention by the MP for Devizes was inevitably viewed as an attack on Mr Cameron's push to move the Conservatives into the political centre ground.

He is the most senior Tory traditionalist so far to go public with criticism of Mr Cameron's approach, although others have expressed concerns in private.

His intervention will be all the more potent because of his ultra-loyal record in three decades as an MP.

The comments provoked fury at Conservative headquarters in a week when the leadership had been hoping to get back on track after a rough summer.

"The challenges facing Britain today have changed and so the Conservative Party has changed too," a spokesman said.

Former Defence Secretary Michael Portillo also hit out at Mr Ancram, insisting he should have kept quiet about his concerns.

Meanwhile, Prime Minister Gordon Brown sought to add fuel to the fire during his regular Downing Street press conference by praising Baroness Thatcher and castigating Mr Cameron for "leadership failures".