The London mayoral race is much more than about who will govern Britain's capital. It's a dry run for the next general election and a barometer of how the Tory party could do two years from now.

If the Conservative candidate Boris Johnson beats the incumbent Ken Livingstone of the Labour Party, he will be the highest elected Tory in all of Britain. His policies will heavily influence the party going into a general election campaign.

The title London mayor seems steeped in tradition but in reality it is a new post created in 2000 and occupied by Livingstone since. The ancient and now mainly ceremonial role of The Lord Mayor of the City of London is a different post.

The Conservatives hope that a victory in London will shatter the Labour Party's already low morale, increase pressure on Prime Minister Gordon Brown and be a springboard for an assault on Downing Street.

Labour, on the other hand, believe that if they can hold on to London, it will signal a change in their recent dire fortunes and reverse a slide in the opinion polls.

In a very real sense, Londoners will be voting not just for their mayor but casting the first ballots of the next general election.