May 2 (Bloomberg) -- Paddy Power Plc, Ireland's biggest bookmaker, said it expects Boris Johnson has won London's mayoral election and has started paying out bets on the Conservative candidate.

Vote counting in Johnson's race with the incumbent, the Labour Party's Ken Livingstone, isn't finished and the results will probably be announced later today. Prime Minister Gordon Brown's party is headed for its worst performance for more than three decades in local council elections, with a British Broadcasting Corp. projection putting it in third place with less than a quarter of the vote.

``After the kick in the ballots that Labour has had overnight, we expect Boris to put the final nail in their local elections coffin,'' Paddy Power said in an e-mailed statement today. ``Boris' backers shouldn't have to wait to have their pockets lined.''

Livingstone is seeking his third term as mayor in a hard- fought battle against Johnson, a Conservative member of Parliament and journalist. Opinion polls showed the two candidates neck and neck after a campaign that centered on violent crime, public transportation and the personalities of the two leading contenders.

``We are fairly confident,'' Paddy Power spokesman Darren Haines said by telephone. ``We are very rarely wrong. Betting is quite a good indicator of what's going to happen. It's often better than opinion polls.''

The decision followed ``strong betting'' on Johnson in the race's final 48 hours, with wagers as large as 5,000 pounds ($9,871) on the 4/11 favorite, the statement said. Those odds mean a winning bet of 11 pounds on Johnson would return 4 pounds of profit.

Paddy Power said the payout will cost the bookmaker just under 100,000 pounds.

To contact the reporter on this story: Loveday Morris in London at lmorris7@bloomberg.net

Last Updated: May 2, 2008 09:56 EDT