Comment: battle has been a road test for the party machines

The lessons of defeat will thus be as important as the lessons of victory.

Ken Livingstone has already presaged the kind of soul-searching that would pervade Labour if he loses, telling the Standard yesterday: "If I lost it would not be because of the argument, it would be because the Tories have run a superior campaign and differential turnout."

That is the political equivalent of the old football commentator's faux pas: "If that one had gone in, it would have been a goal."

But aside from the buck-shifting, Mr Livingstone is articulating something many government strategists have watched with distress: he had the benefit of experience as one of the great pavement politicians of his era and the once mighty New Labour machine to come to his aid, and is nonetheless fighting for his career.

The Johnson campaign - a motley crew of young PR women, a jobbing Australian trouble-shooter in Lynton Crosby and Dan Ritterband on loan from Central Office - have brought their man into hot contention for the job, when he had started as a rank outsider. On the other side, Tessa Jowell, an impeccable New Labour figure with a sound working knowledge of London political from her days in local government, was thrown into the fray when the polls started to tilt decisively to Mr Johnson.

She has never looked comfortable in a role which entailed making excuses for the Mayor's wilder statements. Ken and New Labour were always uneasy bedfellows.

Party insiders also betray some unease about working overtime for a man who has described "grinding New Labour into the dust" as the finest moment of his career.

"To be perfectly honest," says one minister, "I turned out for him with gritted teeth and a clothes peg on my nose. It's only the thought of Boris that drives me on."

For the Tories, the spoils of victory would be put down to a change in the political wind and an omen of good times ahead. At the very least, a London victory will show that Mr Cameron has succeeded in " detoxifying" his brand in the metropolis.

That result would bode ill for Labour in the South-East marginals.

They must also be aware that the Boris campaign has often been fought on a wing and a prayer. In a general election, there will be far greater scrutiny given to inconsistencies on immigration, the balance of the pro-business case and local planning controls, and other choices a government-in-waiting cannot fudge for long. If he fails to prevail, it will be back to the drawing board for Mr Cameron's tactics of choosing high profile younger figures for prominent battles.

Mr Johnson has been the beneficiary of a fast-moving campaign with clearly targeted areas in outer London to provide his "core".

He has, however, stuttered in debates under sustained questioning. Strategy director Steve Hilton and the Cameronian shock troops need to act on the consequences of that: namely that a new form of Tory politics that is flexible and protean also needs a bottom line which does not wander into vagaries under pressure.

One of the surprises of the contest has been the confident performance of Brian Paddick. He may be the third wheel on the bicycle, in terms of the final result, but he has kept up with the speed of the campaign with a far smaller support team and elbowed his way into the debates.

Hampered by having only one strong suit - crime - and a semi-detached relationship with the national Lib-Dems, he has given the third party the voice in the London race it lacked last time. Mr Paddick is a one-man band, but one we will hear more of, whoever rules City Hall after today.