Conservative leader David Cameron has said Boris Johnson's victory in London showed his party was ready to "step up for Britain".
Seizing the London mayoralty put the final touch to a day of success for Mr Cameron in local council elections, which saw Tories gain 260 councillors and a projected 44% share of the national vote.
The Tory leader said: "Three years ago, the idea that the Conservatives would win London and build up a 20-point lead across the county would have been literally unthinkable.
"London is one of the most diverse, vibrant, successful and important cities in the world, and in Boris Johnson it is now has a Conservative mayor.
"Boris ran a serious and energetic campaign and deserves his remarkable victory.
"Britain is crying out for real change and it is the Conservative Party - modernised and united - that is winning the battle of ideas.
"We've shown there is an alternative. We must now prove it. But I believe that my party - the Conservative Party - is ready to step up for Britain."
Metropolitan Police Commissioner Sir Ian Blair congratulated Mr Johnson on his election.
Sir Ian said: "I look forward to developing an effective working relationship between the Met and the new mayor.
.....continued below"Tackling crime and delivering a responsive and quality policing service is a priority for Londoners and this was reflected in the high profile given to these issues during the election campaign.
Conservative leader David Cameron has said Boris Johnson's victory in London showed his party was ready to "step up for Britain".
Seizing the London mayoralty put the final touch to a day of success for Mr Cameron in local council elections, which saw Tories gain 260 councillors and a projected 44% share of the national vote.
The Tory leader said: "Three years ago, the idea that the Conservatives would win London and build up a 20-point lead across the county would have been literally unthinkable.
"London is one of the most diverse, vibrant, successful and important cities in the world, and in Boris Johnson it is now has a Conservative mayor.
"Boris ran a serious and energetic campaign and deserves his remarkable victory.
"Britain is crying out for real change and it is the Conservative Party - modernised and united - that is winning the battle of ideas.
"We've shown there is an alternative. We must now prove it. But I believe that my party - the Conservative Party - is ready to step up for Britain."
Metropolitan Police Commissioner Sir Ian Blair congratulated Mr Johnson on his election.
Sir Ian said: "I look forward to developing an effective working relationship between the Met and the new mayor.
"Tackling crime and delivering a responsive and quality policing service is a priority for Londoners and this was reflected in the high profile given to these issues during the election campaign.
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