The mayor of London's visit to the Birmingham gathering is emerging as a logistical headache for Number 10, where there are worries that Johnson will outshine the prime minister and emerge as the unquestioned darling of the conference.
As well as delivering a keynote speech on the Tuesday morning – the day before Cameron's address – the mayor is also down to speak at what will be a packed Conservative Home fringe meeting the evening before, to hail his achievements in 2012. The fringe event, which the editor of Conservative Home and one of Cameron's most consistent critics, Tim Montgomerie, will also address is entitled, "Boris Johnson's 2012. Re-elected and Olympotastic".
In the aftermath of the Olympics, Johnson's popularity both within the Conservative party and with the public at large has soared amid signs some Tory MPs and activists would like him to return to the House of Commons and replace Cameron as leader.
A YouGov poll on Saturday showed him to be Britain's most respected political leader. Johnson had a net score on "respect" of plus 25 points, calculated by subtracting those who extend him little or no respect from those who accord him a great deal or a fair amount of respect. By contrast Cameron scored minus 18 points and Nick Clegg minus 52.
Last week Boris stole the limelight at a parade to mark the end of the Paralympics, where a crowd cheered and roared his at times irreverent speech as Cameron looked on. While the mayor has insisted he is entirely loyal to Cameron and has no intention of taking his job, his decision to talk up his own success in getting re-elected against Ken Livingstone when he is in Birmingham is sure to raise eyebrows.
The Observer understands that talks have taken place in the past few days about the delicate balance that Johnson must strike at the conference. "We know he can't overplay his hand," said an MP supporter. "He knows that too, but he is not one to go quiet."
It has been agreed that he will talk about winning in hard times, how best to take on and beat Labour, and the lessons to be learned from the Olympics.
After the conference season Johnson will address the 1922 committee of Tory backbenchers on 7 November, at the invitation of its chairman, Graham Brady. He is expected to talk about harnessing the Olympic spirit and – again – how to win in London.
The surge in popularity for Johnson comes as about a dozen Tory MPs have signed letters to Brady calling for a leadership contest. MPs are deeply divided on whether they think the mayor could become leader. Some younger members believe he would lift the party's spirits and give it a sense of direction that they feel is lacking.
Johnson has a record of causing trouble for Cameron at party conferences. In 2006, after Cameron had praised the TV chef Jamie Oliver, he took the opposite line and caused a media storm as the leader's team was trying to brief journalists.
And in 2009 he spoke of the need for a referendum on the European Union when Cameron was desperate to shut the issue down. Furious Cameron aides sent Johnson angry messages, including one in Italian which read "Revenge is a meal best eaten cold."
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image: © University Hospitals Birmingham