John Rentoul: What can Boris Johnson be up to?

Boris Johnson is up to something. He usually is, and it is usually the same thing. I am not talking about his private life, but about his ceaseless positioning to take over from David Cameron as prime minister. It seems improbable that he might succeed, yet he persists with such enthusiasm that he makes us wonder.

Last week he was asked why Sir Paul Stephenson, the Metropolitan Police Commissioner, resigned because his force had hired someone who used to work for the News of the World, when David Cameron, who had hired Andy Coulson, was still in his job. "I'm not here to discuss government appointments," he said, at a news conference. "Those questions you must address to government. I don't think there's a very clear read across. This is a matter you must address to No 10."

When some of my colleagues did precisely that, they were told that Boris was Boris. But within an hour, they were told that Boris, although he was still Boris, would be putting out a statement clarifying his comments. If you look up "clarify" in the Dictionary of Political Euphemism, you will find it involves a "politician who has been sworn at in private and forced by a more powerful politician to retract damaging words". Except that, as the day went on, no clarification came.

My colleagues decided this was in turn a matter they must address to City Hall. But Johnson's spokesman said a statement was unnecessary: "Mr Johnson thinks David is a top guy who has to make some very difficult decisions. It is totally mischievous to suggest that he doesn't fully support him." Given that mischief is Boris's middle name (between Alexander and de Pfeffel), this was a case study in cheek.

The mayor has had an interesting phone-hacking scandal. He was one of those told in 2006 that his name was on a list, suggesting that someone had listened to his voicemails. But he was not keen to do much about it. Last year he said there was no need for a further police investigation, and dismissed suggestions that top people at the News of the World had known that hacking was common practice as "codswallop". He accused Labour of a "politically motivated put-up job", and said the Opposition was pressing it "simply in order to score party-political points against the Prime Minister's press spokesman". Such unexpected loyalty to Cameron should have excited suspicion. It was almost as if Johnson did not want attention drawn to his own phone messages.

Last week, however, Johnson suddenly became more activist in the affair. I do not believe that he forced Sir Paul Stephenson to resign as commissioner last Sunday, but on his own account he did not beg him to stay. Thus, the mayor again exploited the crossed wires of accountability that connect the Metropolitan Police Commissioner both to him and to the Home Office. When he was elected Mayor of London in 2008, Johnson forced Sir Ian Blair out by expressing no confidence in him, which trumped Jacqui Smith, the Home Secretary, who wanted to keep him.

By going on the Today programme on Monday, though, Johnson certainly gave John Yates, the Met's assistant commissioner, a violent push towards the exit. He was asked about Neil Wallis, the former deputy editor of the News of the World, known as "Wolfman", who had been hired by the Met as a locum spin-doctor, and said: "I think it was wrong that we weren't told about the relationship between the Met and Neil Wallis." Johnson was also asked about Yates: "Clearly there are questions about his links with Neil Wallis." Yates resigned that afternoon.

Yates is not my favourite policeman. Contrast, if you will, his assiduity in taking eight hours to decide that there was no need to reopen the police investigation into hacking with his year-long inquiry into the alleged attempted sale of peerages by Tony Blair and Lord Levy, which never had the remotest prospect of laying charges.

But I do not see that the Met's counter-terrorism operations in the year before the Olympics are strengthened by replacing Yates with Cressida Dick, who may have been cleared of personal blame for the killing by the police of Jean Charles de Menezes in Stockwell in 2005, but who was in charge when it happened.

Johnson's handling of the police is symbolic of his mayoralty: full of bombast and colour, but making little difference in practice. He has given his name to some clunky bicycles planned by Ken Livingstone, but he has failed to sort out the Tube drivers' union, which is what a lot of Londoners elected him to do.

He has used his office to position himself to the right of the Prime Minister on some things, such as economics, Europe and crime. He dissented from government policy on the 50p rate of income tax, the lack of a referendum on the Lisbon treaty and Kenneth Clarke's plan to cut sentences. And he has positioned himself to the left of Cameron on other things, calling the "broken society" slogan "piffle" and warning that housing benefit cuts could cause "Kosovo-style social cleansing".

We know what he is up to, and he is the bookies' favourite as "next permanent leader of the Conservative Party", at 4/1, ahead of George Osborne at 6/1. But it still requires quite a stretch of imagination to see how it might happen. If he is re-elected as Mayor of London next year, which I regard as a formality, he would have to engineer his return to the Commons in a by-election after the end of his second term in 2016.

Even as a two-time winner in the largest electorate in the country, and a national personality, it will be hard to persuade fellow MPs that he is what they need. Many resent his grandstanding. The word "buffoon" has been used (Chambers Dictionary: "a person who sets out to amuse people with jokes"). A buffoon may be popular as mayor but not as prime minister. As we saw last week, that is not going to stop him trying.

independent.co.uk/jrentoul