There can be few political contests whose outcome was quite as predictable as the battle for the Tory candidacy to take on Ken Livingstone for the job of Mayor of London.

Boris Johnson won by a mile. The idea of an open contest to decide the candidate democratically, with all Londoners eligible to participate, was undeniably well-intentioned. But the worth of any such contest depends on the credibility of the candidates, and the line-up, before Mr Johnson saved the party's face by entering the fray, was markedly unimpressive.

The Conservative leadership can breathe freely again - its man for the London mayoralty is universally recognised, media-savvy and unquestionably adds to the gaiety of national life.

These qualities are all admirable but they are not enough in themselves to guarantee victory over one of the most consummate and brilliant operators in British politics, Ken Livingstone. Mr Johnson is, beneath his affectation of disorganisation and genuine showmanship, a shrewd and thoughtful individual. He must now show that he has the sobriety and consistency to address the fundamental choices facing the capital. Of these, transport is the most urgent. Mr Johnson must demonstrate that he has a range of workable policies on the core issues - from modifications to the congestion charge to securing funding for vital Tube improvements - which will withstand close scrutiny.

There are, Heaven knows, a number of issues on which the Mayor is vulnerable. His approach to crucial planning issues is authoritarian and his championship of high-rise buildings divisive. His empire-building is a poor use of council taxpayers' money. His quasi-foreign-policy initiatives for London involve consorting with some exceedingly problematic individuals. His popular extension of free public transport for younger people sits badly with exorbitant fare rises for everyone else.

There is, in short, everything to play for. It is now for Mr Johnson to prove that he has the seriousness to measure up to this challenge. If he does, he could win.