On May 1, London held its third mayoral election using a form of instant runoff voting. The Conservative Party's Boris Johnson defeated Labor Party incumbent Ken Livingstone, winning 53% to 47% in the instant runoff. This election had the city's best turnout ever -- a 20% increase compared to the 2004 elections.

Also known as the "supplementary vote," the London system limits voters to a first choice and second choice and moves directly to a second round of voting between the top two finishers. It was first implemented in 2000 after 72% of the London electorate approved direct mayoral elections with IRV by referendum. The system is increasingly popular in England: 12 cities use this form of IRV for mayoral elections.

Londoners also elected the London Assembly (14 members elected directly from constituencies and 11 seats at-large) through a mixed member proportional system. The Conservative and Labor Parties swept the 14 winner-take-all seats, but smaller parties won a total of six seats due to proportional voting.