Mr Cameron wants to see a fall in the number of ministers

He will use his party's annual conference, which starts in Bournemouth on Sunday, to stress his commitment to developing serious policy ideas.

There will be no specific policy announcements at the four-day rally, a Tory spokesman confirmed.

But Mr Cameron is expected to focus on the work of the party's six policy groups established last year.

It comes as Mr Cameron set out proposals to "clean up" British politics, which would involve ending the practice of MPs setting their own salaries.

He also backed a cap on the number of ministers and special advisers a government can appoint, and wants to hand investigation of ministers' conduct to an independent body.

'Detailed policy'

A spokesman said Mr Cameron intended to use the party's annual conference to hit back at claims by his Labour and Liberal Democrat opponents that his leadership was just a "PR exercise" and that he had no substance.

CONSERVATIVE WEEK Sunday Senator John McCain David Cameron Monday Hot topic: Marketing to children Public services debate David Davis, Crime debate Hot topic: Cheap flights Environment debate Tuesday Hot topic: Alcohol and drugs Social justice debate Business in society George Osborne, economy William Hague, Liam Fox, foreign affairs Devolution debate Wednesday Culture of creativity Hot topic: Globalisation Global poverty debate Leader's speech Analysis: New look rally?

He is expected to use his closing speech on Wednesday to give more details about the work of his six policy groups - but he would not be forced into making "policy on the hoof", his spokesman stressed.

The policy groups - on social justice, democracy, national and international security, quality of life, reform of public services and economic competitiveness - are due to report next summer.

Their findings will then be considered by the shadow cabinet, who will draw up the party's next manifesto.

The format of this year's Conservative conference is designed to showcase the party's new direction.

Shadow cabinet members will give much shorter speeches than usual and open up their subjects to debate in the hall.

There will also be a series of "hot topic" policy debates, starting on Monday with a discussion on whether it is time to ban marketing to children.

Delegates will be able to vote on these debates using "X-Factor"-style electronic keypads.

They will also be able to comment on speeches and debates by sending text messages to a big screen above the platform - although these will be screened by party workers for obscenities or libels.

HAVE YOUR SAY When will we see a determined and strong opposition? Lionlen, Salisbury Send us your comments

The party has also invited a series of outside experts to take part in debates, including Big Issue founder John Bird, the deputy secretary-general of the United Nations, Mark Malloch Brown, and children's campaigner Camila Batmanghelidjh.

Centre-right coalition

The idea is to transfer some of the passion and energy of conference fringe meetings to the main hall, a party spokesman said.

US Senator John McCain, a frontrunner for the 2008 Republican nomination, will address the conference before Mr Cameron on Sunday.

There will also be video messages from the leader of France's governing UMP party, Nicolas Sarkozy, and incoming Swedish president Fredrik Reinfeldt.

Mr Reinfeldt - dubbed the "Swedish David Cameron" - recently ended a long tradition of Social Democratic rule in Sweden, with a centre-right coalition headed by his Moderate Party.

"My simple message to you is this: We changed, and we won the election," Mr Reinfeldt will tell Tory delegates.