Now Ken has his eyes on No 10

A loose coalition of "urban guerrillas" - with a small politically motivated core - "reclaims the streets" of London, and thumbs its collective nose at the Westminster establishment. But this weekend the hangover is just beginning. While the clean-up from those anarchists' antics on Monday was complete after a couple of days, that other snub to the government elite - electing Ken Livingstone as Mayor of London - is a mess that will take rather longer to sweep up.

The electorate's independence of mind is to be applauded, even though turnout was rather lower than feared. This newspaper would be the last to criticise those who decided to vote for a candidate from outside the lumbering party machines. Many - perhaps most - of those who voted for Mr Livingstone on Thursday did so for laudable reasons. They felt, rightly, that both major parties deserved contempt for their shambolic handling of candidate selection, and that London needed a strong and non-partisan voice for its first mayor. But we fear that the result is not to be welcomed; that Citizen Ken may prove less attractive in power than as an outsider.

Of course Ken Livingstone is not the unreconstructed, stuck-in-the-1970s, mindless Stalinist that his opponents would have you believe. He has, wisely, dropped much of his old rhetoric and alliances, and now stands as a vaguely leftish Keynesian: hardly the stuff of tabloid nightmares. But our concerns about "the People's Ken" lie not so much with his (rather vague) policies for the mayoralty, but with the likelihood that he will use the office to further his greater ambitions, and in doing so will betray the Londoners who voted for him.

Mr Livingstone hopes one day to be Prime Minister. This is a worthy ambition shared by many politicians. But we fear that he will take the opportunity he now has, and the platform that the mayoralty offers, to encourage dissent and cause trouble for the two men who most stand in the way of that ambition - Tony Blair and, more particularly, Gordon Brown. Mr Blair will be in the firing line because he would prevent Mr Livingstone's re-entry to the Labour Party, a prerequisite for the eventual premiership. The Chancellor's crime is that he, rather than Mr Livingstone, is the current favourite to succeed the Prime Minister. Mr Livingstone now has a golden opportunity to chip away at Mr Brown's support, particularly among trade unions. To use the London mayoralty for such personal petty posturing would be a tragedy - but the signs are not good. Already, Mayor Livingstone's attacks on the Government seem focused on Mr Brown and Mr Blair: for the defeated Labour candidate, Frank Dobson, he has only conciliatory words and job offers.

We hope that we are wrong about Ken Livingstone. It would be churlish after only three days not to offer the new Mayor of London our congratulations. But we must also request that he uses his enormous mandate to better the prospects of all the people of London, not just those of Ken Livingstone.