London Mayor Boris Johnson will use his high-profile address to the Conservative conference to plead for more help for small businesses, urging the Government to create the conditions for them to become "the gold medallists of the global economy".

After his rapturous welcome to the conference in Birmingham on Monday night, Mr Johnson's platform speech is expected to be the highlight of Tuesday's events, and will be pored over by commentators looking for hints of a challenge to Prime Minister David Cameron.

Mr Cameron has insisted that he was not worried about the "rock star status" the Mayor has attained since his re-election to City Hall and his successful stewardship of this summer's Olympic and Paralympic Games in London.

But gossip about Mr Johnson's future has filled the bars and corridors in Birmingham, after polls suggesting he could deliver a major boost to the Tories if he took over as leader.

Extracts from his speech released before he took to the stage suggest that he will back the Prime Minister's promise to help the "strivers" in society who work hard to get on in life.

Mr Johnson is expected to tell delegates: "I am a Conservative. I believe in a low-tax and low-regulation economy, and I believe that, as far as possible, government needs to make life easy for those who get up at five to get their shops or businesses ready - the strivers, the strugglers, whatever the vogue word is for them today.

"We know who they are - and there are many in this room - the backbone of the UK economy."

Making his plea for help for small businesses, Mr Johnson is expected to add: "Britain is a nation of small and medium-sized enterprises and they make up 75% of the London economy.

"And it is these businesses that have the capacity to grow, to take on young people, to expand and become world-beaters.

"And we need to think, every day, what we can do to create the right conditions for them to flourish and to become more than medium-sized - to become the gold medallists of the global economy."