The former speaker, John Bercow, was re-elected and ceremonially dragged to the speaker's chair in a tradition dating back to centuries past, when previous holders of the office could be executed by thin-skinned monarchs.
Bercow said that he wanted lawmakers to be "part of the cast, not merely an audience" to government actions and promised to champion the rights of backbench MPs.
He also cracked a joke about the words he would like on his "political tombstone" -- a reference to a widely mocked Labour campaign stunt that involved carving policy pledges into a block of limestone.
"I've lost a coalition partner but I've gained a number of new friends," Cameron said to loud cheers from Conservative MPs, after his party won 331 out of 650 seats in the House of Commons in the May 7 election.
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Cameron also promised more local powers for Northern Ireland, Scotland and Wales, saying that the Scottish legislature would be the "strongest" in the world.
He noted that the new parliament was "more diverse and more representative" than ever before, including the first MP of ethnic Chinese background and the first female cabinet minister of Indian origin.
"We applied for the job but we didn't get it. But we have got a very important job of being the official opposition and we will be fearless and effective in doing that," she said, despite divisions within Labour over the direction the party should take.