Boris Johnson
London Mayor Boris Johnson will be pressed to reveal his Commons plans

Machiavelli's advice to "keep your friends close and your enemies closer" has become a political cliché for the very good reason that it is just the best possible approach to someone like, for example, Boris Johnson.

And David Cameron has followed this centuries-old tenet to the letter by declaring he wants the London mayor back in the Commons as soon as possible, and certainly in time for the next general election.

He says there is "nothing ignoble" about Johnson wanting his job and that he wants him "on the team" for the 2015 poll. And, for the first time, he has said there would be no problem Johnson serving as both mayor and an MP.

Until now there has been some confusion about how realistic it would be for the mayor to do both jobs, a situation that has suited Johnson. Although it is pointed out his predecessor Ken Livingstone did both jobs for a while and there is no rule banning it.

Johnson, meanwhile, has adopted his usual mock-befuddled approach and found a dozen different ways of not properly answering the question. But, thanks to Cameron's latest intervention, that is becoming an increasingly untenable position.

If your leader calls, you really should present yourself for service. For Johnson to simply brush aside Cameron's entreaties, no matter what he fears may lie behind them, strays beyond rude and towards disloyal.

So the prime minister's calculated wooing of his old Eton and Oxford pal has put the ball firmly in Johnson's court.

Interviewed for the Sun newspaper by guest editor, actor James Corden, Cameron said: "I want him to get back in parliament. I think he's great. It's a bit like football - if you have got a great striker you want him on the pitch.

"It's up to him. He can complete as mayor, or he can come back to the house. I want him on the team. He has an amazing capacity to defy gravity that other politicians don't. And also he is fun.

"I find him genuinely amusing," he said, adding, "Underneath there is quite a serious person beavering away."

Asked about the Tory leadership, he added: "It wouldn't be a great job to have if people didn't want it. There is nothing ignoble about wanting my job."

What this is really all about is the Cameron-Osborne axis' campaign to stymie Johnson's leadership ambitions by linking him directly to the election campaign so that, if the ship goes down, he goes down with it.

Having him on the team will also ensure they can keep a very close eye on him. He would have to report to the prime minister on a regular basis rather than retain his lofty independence.

It is widely believed Johnson's strategy is to play it long, wait for the expected failure by Cameron to win an outright majority in 2015 and then swing in to a conveniently vacated safe seat, like Flash Gordon on a tripwire, to drag the party back to electability.

To do that he must ensure he is as little tainted as possible by the election campaign, which will be difficult if he is "on the team".

What makes Cameron's latest remarks notable is that they come amid signs the low-level war between the Johnson and Cameron/Osborne camps is intensifying with education secretary Michael Gove leading the briefing war against Johnson on behalf of the prime minister and chancellor.

Previously Cameron had simply said he would be delighted to see Johnson back in the Commons but insisted it was "up to him". Now he has gone further by making it clear he believes Johnson should get back into the Commons before the election.

And that has put the mayor firmly on the spot.