David Cameron hails Boris Johnson's London mayoral win
Prime Minister David Cameron has said he is "delighted" with Boris Johnson's re-election as London mayor.
He said the Conservative candidate fought "a very strong campaign", and "now what matters is working together for the good of London".
Mr Johnson outperformed his party as a whole in the local elections, but said the mayoral election was simply "a contest between two propositions".
The Tories suffered heavy losses, with Labour seizing control of 32 councils.
Mr Johnson was sworn in at City Hall at short time ago and thanked "the people of London for giving me a second mandate".
The mayoral contest was much closer than many people had expected.
Mr Johnson gained 44% of first preference votes, to Ken Livingstone's 40.3%. After second preferences came into play, Mr Johnson gained a total of 1,054,811 votes, or 51.5%, to the Labour candidate's 48.5%.
Lib Dem Brian Paddick saw his vote collapse and he was beaten into fourth place by Green Jenny Jones, with independent Siobhan Benita fifth.
Speaking at City Hall on Saturday, Mr Cameron said: "I think it was a very strong campaign by Boris. It was based on his record, on the excellent things he has done as mayor and I am delighted to congratulate him.
"It was a campaign the whole Conservative party got behind.
"I enjoyed campaigning with Boris, but now what matters is working together for the good of London, as prime minister, as mayor, and that is exactly what we are going to do."
Mr Johnson said it was "a hard-fought, long campaign" and he was "grateful" to the Conservative Party for supporting him.
"I think we were able to reach people across the city with a message which resonated with them in tough times."
Asked why he had done so much better than the Conservatives elsewhere, he replied: "A mayoral contest is inevitably a contest between two propositions.
"Basically, proposition A was go back to the 1970s or 1980s and proposition B was go forward with investment in creating jobs, growth, in the most dynamic city in Europe."
Elsewhere in the local elections:
- Labour gained 823 councillors nationally, as the Tories lost 405 and the Lib Dems 336
- Labour and the SNP made big gains in Scotland, but with no one party managing to secure a majority in most councils, talks are due to begin to work out who will form ruling administrations
- Labour made substantial gains in Wales, taking 10 out of the 21 councils including Cardiff, and prompting leader Carwyn Jones to suggest his party could win outright in the Welsh assembly in 2016
- The Conservatives blamed their losses on "mid-term blues", with David Cameron promising he would not change course
- The Lib Dems now have fewer councillors than at any time since the party was formed in 1988, but Nick Clegg said
- Voters in Birmingham, Sheffield, Newcastle, Wakefield, Manchester, Nottingham, Bradford, Leeds and Coventry rejected the mayoral system - but Bristol voted in favour and Doncaster voted to keep their mayor
In his losing speech, Mr Livingstone announced his apparent retirement from frontline politics, saying "this will be my last election".
Later, he apologised for failing to secure victory, but said the campaign had been "vicious and unpleasant" and blamed "incredibly slanted" media coverage which he said had led to his key pledge - to cut fares - being "marginalised".
He branded Mr Johnson a "do-nothing mayor" and said he had merely "carried on opening the things I started".
"If we have another four years like that, then by the end of this decade London will be insufferable. The population's growing, you've got to massively expand housing, you've go to expand the transport capacity.
"It will be the mayor two down the road from here who then faces a real crisis."
But speaking as he was sworn in, Mr Johnson promised to "work his socks off" and "stand up for London and Londoners even if the plaster sometimes comes off the ceiling in Whitehall".
There has been speculation that Mr Johnson could be a future Conservative Party leader, but he told the BBC he was dedicating himself to London and people could "take it for granted" that he would not stand as an MP at the 2015 general election.
The Conservatives lost several councils across the country - including Plymouth, Southampton and Harlow - to Labour in Thursday's elections.
Labour also took two high-profile scalps at the London Assembly - deputy mayor and Conservative Group leader Richard Barnes, and chairman of the London Fire Authority Brian Coleman.
But Employment Minister Chris Grayling said "this always happens to governments mid-term".
"Some of the policies you've put in place have yet to come to fruition, or have yet to... demonstrate their benefits, and we've taken tough decisions about dealing with the deficit," he said.
"All of those things have an impact on the public's view of the government of the day... [But] we're not going to be blown off track by one poor set of local election results."
Shadow attorney general Emily Thornberry said the government was "not doing the right thing" and had "no plan B" to get the economy growing and unemployment down.
"I think that we, as the Labour Party, are rebuilding trust... We're on our way, we're going in the right direction, but we've still got much more work to do."
She said Ed Miliband was "clearly growing into the job", adding: "Nobody comes off the peg a ready-made prime minister."