UPDATE 7-Brown's party routed in UK elections, loses London

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By Tim Castle and Katherine Baldwin

LONDON, May 2 (Reuters) - Britain's Labour Party suffered its worst local election defeat on record and lost control of London on Friday, forcing Prime Minister Gordon Brown to rethink his strategy to avoid losing the next national poll.

Conservative Boris Johnson, a journalist-turned-lawmaker prone to gaffes, wrested the prized post of London mayor from Labour's maverick Ken Livingstone, who has run the sprawling metropolis of some 7.5 million people since 2000.

The election results were a major blow to Brown, who enjoyed a brief honeymoon with voters after he took over from Tony Blair, but has since been beset by economic turmoil, industrial unrest, administrative blunders and an image problem.

Contrite Labour ministers and lawmakers said the government had failed to address Britons' fears of rising food and energy prices, higher mortgages and a possible housing market slump.

The question now is whether the rout was just mid-term blues from which Labour can recover before the next general election, due by mid-2010 at the latest, or whether the tide has turned towards the Conservatives.

Accepting the post, Johnson said he hoped his victory represented a turning point for the party which has been in opposition since Blair swept to power in 1997.

"I do not for one minute believe that this election shows that London has been transformed overnight into a Conservative city but I do hope it does show that the Conservatives have changed into a party that can again be trusted," he said.