On the face of it, the choice at Britain’s coming election is straightforward enough. Do the voters want to put the Conservative’s David Cameron back in Downing Street or do they prefer Labour’s Ed Miliband? Is the country leaning rightward or leftward, towards continuity or change? Alas, politics is rarely that simple.

Britain has left behind the days when two-party politics all but guaranteed decisive one-party government. Allegiances have splintered. Insurgent nationalists, of the Scottish and English varieties, are on the march. The Tories and Labour have retreated into regional redoubts. The political centre ground stands empty.

Messrs Cameron and Miliband have been joined by a third player in the race for No 10. And I do not mean Nick Clegg, Mr Cameron’s Liberal Democrat coalition partner. The safest bet on the election outcome is that Clegg’s party will be roundly punished for joining forces with the Conservatives in 2010. That is unfair, but it is the common fate of smaller parties in coalition politics.

No, the prince across the water with his eye on Cameron’s crown is a Tory. He is not yet an MP and, for now, pledges absolute fealty to the king. Everyone at Westminster knows he does not mean a word of it. For now, Boris Johnson sits in City Hall, across the Thames from the House of Commons. If London’s mayor returns to parliament on May 7, the only question on his mind will be how soon to grab the prize. It is no more than slightly fanciful to imagine he could be prime minister within the year.

Cameron learnt this week that stating the obvious can be a mistake. As the glasses clinked at convivial end-of-parliament parties across Westminster, Tory MPs were baffled as to why, on the eve of his bid for re-election, the prime minister had volunteered to the BBC that he would not be putting himself forward for a third term in 2020.

The remark was presumptuous on two counts: first for taking for granted the voters’ endorsement in May; and, second, for assuming his own party will permit him to choose the timing of his departure. An outright victory on May 7 might, just might, afford him that luxury, but the polls suggest that even if the Conservatives beat Labour, they will fall short of a governing majority.

Though more popular in the country than a Tory party seen to take ideological delight in austerity, Cameron is not held in high esteem by Tory MPs. All prime ministers suffer the wrath of the has-beens and never-has-beens, but the dislike of Cameron runs wider. The eurosceptic right says he lacks all conviction; a smaller rump of modernising centrists say he has failed to shed the Conservatives’ reputation as the nasty party. An imperious personal manner and obvious disdain for lesser mortals scarcely help Cameron’s cause.

Prime ministers do not have to be popular. Margaret Thatcher made do with often grudging respect. They do have to be winners and, so far, the Tory election campaign has not gone to plan. Cameron’s colleagues confessed they had expected to have pulled well ahead of Labour by this stage. Instead, public support for both parties has been stranded in the low 30s.

Clear divide

Cameron’s performance in a set-piece television interview fell short of the sizeable advantage he has held over Miliband in leadership ratings. The Labour leader may not be quite the pushover the prime minister imagined. Tory strategy has been subcontracted to the sharp-talking Australian pollster Lynton Crosby.

Crosby’s insistence that the party talk only about leadership and economic competence may prove a costly mistake. One Tory MP was heard to complain that Crosby had not won over a single Labour voter.

There lies Johnson’s strength. The mayor has what the psephologists call “reach”: a personality that appeals beyond the Tory tribe to voters who might otherwise back parties of the centre-left. Miliband, like the prime minister, is pitching to his core supporters. This mutual failure to reach across the divide may well deny both parties an overall majority — and in the process see Johnson seize the Tory crown.

If Miliband makes it to Downing Street, Cameron will be gone within days. What intrigues many Tory MPs, though, is the possibility of an early leadership contest even if he manages to hang on in No 10 at the head of another coalition or a minority government. Those who think the Tory party would not dare move against a sitting prime minister have forgotten what happened to Thatcher in 1990.

Daydreaming about 2020, Cameron mentioned George Osborne,the chancellor, and Theresa May, the home secretary, as other contenders for the eventual leadership. Johnson does not want to wait another five years and Osborne and May may also soon enough conclude that their leadership prospects are likely to diminish over time as challengers emerge from a new generation of Tories. As the author of the government’s economic strategy, Osborne should be the frontrunner, but he badly lacks personal political skills.

Johnson is a Cavalier to the chancellor’s Roundhead. Like Nigel Farage of the UK Independence party and the Scottish National party’s Alex Salmond, the mayor is a professional politician adept at sharing public contempt for, well, professional politicians.

None of which is to say Johnson is well suited to the role of leader of the opposition, let alone that of prime minister. He views Cameron as his intellectual inferior, but carries a lot of baggage of his own — a colourful personal life, repeated tangles with the truth and an aversion to work. He is a better self-publicist than thinker. The tedious allusions to a classical education are fancy wrapping paper for an approach to politics that lacks weight and seriousness.

This may not worry Tory MPs. Short of an outright victory in May they will be looking for a leader with “reach”, someone who can win elections. Johnson, his friends say, is waiting for the call.

Financial Times