Isabel Oakeshott: Boris Johnson needs a David Cameron victory to keep his plan for the top on course

The Tory leader and London Mayor planned to spend a morning campaigning together and were travelling to their first engagement by bus. It was a little after daybreak when Cameron pitched up at Johnson’s home to collect him, looking immaculate in a bespoke suit and shirt so white it almost glowed. The Tory leader was bang on time and ready to go. Johnson, however, was nowhere to be seen. An embarrassed aide scuttled around the Mayor’s messy kitchen searching for clean mugs to make coffee while they waited.

Eventually he materialised looking characteristically dishevelled (“no collar stiffeners, wet hair, missed a few bits shaving” I am told) and the pair set off for the bus stop.

“What’s the fare to central London?” Cameron asked the Mayor.

“Uh, £1.10 or £1.20 — something like that ...” Johnson replied vaguely.

“You should know things like that, Boris,” Cameron chided.

“Do you?” Johnson retorted.

“Oh yes,” Cameron replied, and proceeded to rattle off a long list of consumer items and their prices.

A pint of milk, a loaf of bread, a pint of beer and a dozen or so other basics — the Tory leader had learned how much they all cost to avoid being caught out by anyone who might seek to suggest he was “out of touch”. When Tory MP Nadine Dorries famously labelled him and George Osborne “two posh boys who don’t know the price of milk” in 2012, she underestimated the former’s impressive memory and grasp of the little things that can trip a politician up. Johnson, meanwhile, has always been happy to busk it — knowing he can charm his way out of a tight spot.

Fast-forward to this campaign and Cameron has learned a sharp lesson about the perils of relying too heavily on a script. Last weekend he briefly forgot which football team he is supposed to support, a mistake that not only made him look foolish but played into the hands of those who seek to portray him as inauthentic. The Mayor may be more accident- prone than the Prime Minister — saying what you think can cause offence — but he would be very unlikely to make a mistake of that type because he would not have pretended to like a sport that did not really interest him in the first place.

In less than two weeks Tories may have to start weighing up whether Johnson’s style is suitable for the top job. For Cameron, there is still all to play for: Tories and Labour remain neck-and-neck. Last week’s Ashcroft National Poll put the Conservatives a few points ahead but a poll by YouGov a few days later gave Labour a two- point lead. Nobody — even those who have studied every bit of polling data — knows what is going to happen on May 7. As Lord Ashcroft likes to say, the keenly awaited voting intention figures are just “a snapshot not a prediction” in any case.

Should Cameron fail to form a government, however, the Conservative party will be plunged into a leadership contest — and will begin considering whether Johnson’s brand of blond bluster is the answer to their travails.

After years of obfuscation, the Mayor — who is running for a seat in Uxbridge and Ruislip — has given up pretending he doesn’t want the top job. When he protests that he wants Cameron to win this election, however, he is speaking from the heart. The truth is that he is playing a longer game and wants Cameron in Downing Street for another two years before he strikes.

For the past 18 months or so he has been quietly war-gaming his path to the premiership with a small team of trusted aides. It has never involved any “plot”. He and his team believe his best chance of making it to No 10 is if Cameron survives until 2017, then steps down voluntarily (the EU referendum would provide a natural cut-off point) by which time Johnson will have finished as Mayor and be in a position to devote his full energy to a leadership contest.

The last thing he wants is five years as Leader of the Opposition, an endurance test which would certainly expose the perils of ad-libbing and give ample time for his charm and novelty factor to wear off.

A source close to the Mayor says: “Nobody wants to be Opposition leader for five years. It is a dreadful job. That’s not the game we want to play.”

Johnson’s genuine commitment to a Cameron victory explains his behaviour during this campaign. “Low-key and loyal” is the way aides describe the strategy — which is why there have not been more photographs of him being mobbed by admirers and posing for selfies with his fans. Though he has not entirely suppressed his personality in the way that he did in the final months of his first mayoral campaign in 2008, he is behaving himself and knows he must not upstage the Prime Minister. So (thus far) there have been no mischievous jibes at “Dave” and he has shown that when it really matters he too is capable of sticking to the script.

Appearing on the BBC’s Andrew Marr show yesterday he was at his best unpolished self — all good humour, bad hair and bad posture — but he played for the team, giving Labour leader Ed Miliband a hard time on policy.

If Johnson is ever to lead the Tory party, sitting it out until 2017 has its own risks. Aides fret about what they call the “king across the water” problem — a concern that people will project unrealistic hopes and expectations onto him while they wait for him to take the crown. Of course, his supporters are confident he will live up to the hype. If any voters are going to be disappointed, however, they calculate that the later it happens, the better.

Lord Ashcroft and Isabel Oakeshott’s biography of David Cameron, Call Me Dave, will be published this autumn