By Ian Dunt
David Cameron has entered No 10 as prime minister, after a day of negotiations in which the Conservatives and Liberal Democrats agreed to form a coalition government.
"Nick Clegg and I are both political leaders who want to put aside party differences and work hard for the common good and the national interest," he said after arriving from Buckingham Palace in Downing Street.
"I believe that is the best way to get the strong government we need - the decisive government we need today."
Mr Cameron was cheered as his car entered Downing Street, although there were also shouts of abuse from the crowds outside.
He confirmed he had accepted the Queen's invitation to form a government and become prime minister before paying tribute to his predecessor, Gordon Brown. Later that evening Nick Clegg was appointed deputy prime minister.
The Conservative leader said Britain had become "more open at home" and "more compassionate abroad" during Labour's time in power.
He said his government would be one which is "built on clear values" of "freedom, fairness and responsibility".
It had been expected that the basis for a deal would require approval by meetings of the Conservative and Lib Dem parliamentary parties due this evening.
But Mr Cameron made clear that he was determined to enter into a formal deal with the Liberals.
"In terms of the future, our country has a hung parliament where no party has an overall majority," he added.
"We have some deep and pressing problems: a huge deficit, deep social problems and a political system in need of reform. For those reasons I aim to form a full and proper coalition with the Liberal Democrats."
Liberal Democrat energy spokesman Simon Hughes said later the agreement would be for a fixed-term parliament of at least four years. Lib Dems will be in government at all levels, he added.
Mr Cameron said he would be "honest" about what his government could achieve and pledged to build a "more responsible society".
He finished: "I want a political system that people can trust and look up to once again. This is going to be hard and difficult work. I believe together we can provide that strong and stable government that our country needs."
On entering No 10 he received a phone call from US president Barack Obama, who congratulated him and told him he was "looking forward to seeing him in June" at forthcoming G8 and G20 summits. The pair discussed Afghanistan, the Middle East peace process and Iran.
He was then driven in the prime ministerial car to the Commons, where he addressed his parliamentary party.
They greeted him with a series of huge cheers and rounds of applause before he told them he was committed to a "strong, stable" government.