''He was the future once," he added, looking across to Blair.
Conservative lawmakers roared as a confident-looking Cameron stood up during the House of Commons session. He grinned when Blair, 52, congratulated him on winning the leadership post.
Cameron, who on Tuesday became the Tories' fifth leader since they last won an election in 1992, says he wants to overhaul the party to shed its image as stodgy and out of touch with modern Britain.
He focused one of his first questions on the environment, an issue not normally associated with the party. But Blair brushed away Cameron's query, accusing the Conservatives of voting against concrete action.
''It is important not merely that we say how much we care about climate change but that we take the action necessary," Blair said.
Cameron later appointed a review group to scrutinize the Tories' positions on social justice, also not one of the party's traditional areas of interest. It was the first step in what he said was a broader review of policy.
''I think the test for all our policies should be: 'What does it do for the people who have the least, for the people on the bottom rung of the ladder?' " he said in a speech at an east London boys' school. ''How can we help those people climb the ladder from poverty to prosperity?"
The weekly opportunity for lawmakers to question the prime minister produces more knockabout theater than reasoned exchanges, but it's an important showcase for party leaders. Although Cameron appeared undaunted, the pressure will remain high as Britons watch to see whether he looks like a potential prime minister.
Cameron succeeds Michael Howard, a Tory veteran known as one of the party's best verbal jousters and widely praised for his performance in the weekly face-offs with Blair. Cameron will face a formidable opponent in Blair, who is far more experienced and renowned for his debating skills.
The Conservative faithful hope Cameron's youth and charisma will help them reconnect with voters and recapture power after three straight election defeats. Some have likened him to a young Blair who took the Labor Party's helm at 41 and made it an election-winning juggernaut.
The Tories believe Cameron will eventually make a tough opponent for Treasury chief Gordon Brown, who is widely expected to succeed Blair as prime minister before the next election.
