12 May 2010 12:08 am
Cameron becomes the country's first Conservative prime minister since the Labour Party, under Tony Blair, defeated John Major in 1997.
Cameron aims to form a coalition government with the Liberal Democrats, he said, after no single party won a majority in elections to the House of Commons last week.
He praised his predecessor in brief remarks outside the prime minister's residence before disappearing into 10 Downing Street with his wife, Samantha. Coalition governments are extremely rare in British politics.
The last time there was a "hung parliament" with no party holding a majority of the seats in the House of Commons was 1974. Coalition talks then between the Conservatives and Liberals failed, and a short-lived minority Labour government took power. (CNN)
File photo taken in 2008