Boris Johnson may be stymied by his own star quality

Pettifogging proceduralists have tried to scatter tacks on the route of his triumphal return to the Commons

Hug your enemies tight. This is one of those frustrating dictums for which there turns out to be no evidence that it was said by a quotable person, in this case Lyndon B Johnson. It is an eternal truth of politics nonetheless, and explains why David Cameron last week again welcomed the prospect of Boris Johnson returning to the House of Commons.

He has said it before, and there was a bit of a fuss a few months ago when friends of Boris denounced friends of George Osborne for "challenging" Boris to stand for Parliament in the 2015 election. Boris doesn't want to be bounced. Like most politicians, he wants to keep his options open. But he shouldn't complain: the Cameron-Osborne bear-hug is a measure of the strength of his position.

The Prime Minister has spotted the obvious possibility that Boris would decide to stand as an MP next year and pre-empted it. This did not require powers of clairvoyance on Cameron's part. Even I, and I have a patchy record in such matters, noticed when Boris was first elected Mayor of London in 2008 that this could be a path to No 10 – which would require a tricky re-entry to the House of Commons.

Not that tricky, though. Conservative association officials everywhere have been quoted as saying how utterly delighted they would be if Magic Johnson should deign to shine his light upon their patch and how (they implied) they wouldn't expect him to visit more than a couple of times a year to cut a ribbon or plant a tree.

Pettifogging proceduralists have tried to scatter tacks across the route of the triumphal return. Boris promised to serve out his second term as mayor, they say. He couldn't be Leader of the Opposition and mayor at the same time, so there would have to be a London-wide by-election, which would annoy voters and turn them against the Conservatives.

To which the Mayor would probably respond: "Details, details and piffle." There is nothing to stop the mayor being an MP. Ken Livingstone – once described by Boris as a "brooding pterodactyl" – held both offices for 13 months when he was first mayor. There is nothing, moreover, to prevent an MP being Leader of the Opposition and mayor of London. It would be a bit strange, but the only rule involved is the one that says there has to be a by-election if a mayoral vacancy arises more than six months before an election. So, if Cameron were to lose the election in May next year and Boris were elected Tory leader in, say, September, he could hold both posts until December, six months before he was due to stand down anyway in May 2016. As Boris said to a German archivist who traced his Bavarian ancestry on BBC1's Who Do You Think You Are? shortly after he became Mayor: "Ich habe der Mystery gecracked."

Procedure is not the problem. The problem for Boris is threefold: will Cameron lose? If so, would Boris get the job? And does he want it? To which the answers are: there's a 40 per cent chance; there's a higher than 40 per cent chance; and, well, obviously. The problem for the rest of us is whether Boris would be the right person to lead a fractious Eurosceptic Tory party in opposing a Miliband government.

He wasn't a great success as a shadow culture minister the last time he was an MP, being forced by Michael Howard, the Tory leader, to travel to Liverpool to apologise for saying its citizens liked to "wallow" in "disproportionate grief" when a hostage was murdered in Iraq. But as leader of a team at London's City Hall, he has managed that most important and most often overlooked qualification for political success: the avoidance of mistakes. He is less popular than he was and, once he re-enters the world of "normal" Westminster politics, would no doubt become less popular still. But he is still one of the Tory party's greatest assets.

The Prime Minister has worked that out. He can see Boris coming and is doing the only thing he can: trying to make the best of it. If Cameron had said nothing and Boris turned up as the Tory candidate for North West Hampshire (where Sir George Young, the chief whip, is standing down), the fuss over the "challenge to the Prime Minister's leadership" would have been a wonder to behold.

Cameron is making his peace with Johnson as did Tony Blair with Gordon Brown before the 2005 election, at a time when Brown was more popular than he was. Cameron knows that Johnson is unusual in that he is a popular politician. In fact, in the Favourability Index compiled by ComRes for The Independent on Sunday, he was the only politician of whom more people had a favourable view than an unfavourable one – 36 per cent to 33 per cent. So it makes sense, as Cameron said last week, to have his star player on the pitch. Boris, like no one else, can help the Tories win and thus dash his own hopes of the leadership.

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