By BBC News Online's Nyta Mann

With the result of Labour's London mayoral nomination battle in and Frank Dobson the winner, Ken Livingstone faces the biggest decision of his political career: should he seize the moment and go it alone?

The man who came second in Labour's electoral college, despite more individuals having voted for him, will be calculating whether he can turn his moral victory into a political one if he runs for mayor as an independent candidate.

The Brent East MP is a master strategist, as shown by his nimble outmanoeuvring of Labour's leadership over the past year in its efforts to stall his mayoral bandwagon.

In the end New Labour got the result Tony Blair wanted, but at the cost of appearing to have gerrymandered the selection process - and making a popular hero of Livingstone.

The former Greater London Council leader will now be weighing up the forces marshalled against him if he stands as an independent.

From unofficial opposition to public enemy

He has already faced the might of the party machine in Labour's selection contest. But in that he was the unofficial opposition. Should he stand alone, Labour will openly declare him their chief public enemy. If he thought the party hierarchy treated him badly before, it is as nothing compared to what they would do to an Independent Ken.

The U-turn charge is the first that will be levelled against him. Didn't he insist all along he would never leave Labour to run independently? And surely he doesn't want to prove Dobson wrong when on Sunday he described Livingstone as a man of his word?

All true, but the accusation that he lied about his intentions may be among the easier obstacles Livingstone must overcome. All he need do is point to the clear majorities by which he beat Dobson among Labour members and those trade unions that held ballots.

He was undemocratically robbed of victory, Livingstone wasted no time in saying; so why shouldn't he run?

As the fall-out over the controversial manner of Dobson's victory continues, Livingstone will be gauging how far his widespread rebel's popularity will take him.

Opinion polls urging him to go for it will be published. The non-Labour left will call on him to stand. Cabbies, commuters and little old ladies will doubtless stop him in the street and demand that he run.

He will also face calls from the press and commentators to stand as an independent in order to give Londoners a clear and real choice. But the long-standing frontrunner for the job knows this will not necessarily translate into backing for him to actually become mayor of London.

A rough press gets tougher

Few politicians have faced such intense and hostile media scrutiny as has Livingstone throughout his political career. But it will get even tougher if he runs for mayor on a Livingstone ticket.

The publicity might help with a further problem, though: money. Labour, nowadays the party of big business and hefty donations, will provide Dobson with the cash, organisation and campaign infrastructure required for his bid to become mayor.

A stand-alone Livingstone will need to raise hundreds of thousands of pounds in a short space of time.

He will also face the charge, taken seriously in Labour circles old and New, of unforgivable disloyalty. The my-party-right-or-wrong factor weighs heavy with many Labour members.

Some who devotedly backed Livingstone in the selection contest, and who now share his fury at the "tainted result", will nevertheless think it beyond the pale for him to stand against the official Labour candidate in May's mayoral poll.

Others, though, would energetically campaign for any Livingstone bid. Left-wingers increasingly disillusioned at much of what New Labour has done, not just in terms of policy but also to the party's internal procedures, may see the mayoral episode as a final defining incident.

By declaring as an independent Livingstone would, under party rules, be deemed to have expelled himself. Likewise any member helping his campaign. Given his support among Labour's rank and file in the capital, a rupture of the London party is a very real prospect.

And last but not least, Livingstone himself would have to deal with the personal wrench of leaving Labour. Unlike some politicians he has, in his time, had a "proper job" - as a hospital research technician at the Royal Marsden. But that was a long time ago; by far his greatest occupation has been as a Labour activist at various levels in the party.

While he has long been a politician who forged alliances across the broad range of the left, rather than restricting himself to Labour alone, he may still find it a heavy burden to be shut out of the party that has been his political home for more than three decades.