Britain's Nice Guy.(International Edition; POLITICS)(David Cameron )

Byline: Stryker McGuire; With David Merlin-Jones

David Cameron looks set to be the next prime minister. But he'll have to put substance over style.

You'd never know it from the graceful, self-confident address he made to a joint session of the U.S. Congress last week, but Prime Minister Gordon Brown is on the way out. That, in any event, is the growing consensus in Britain. The polls and the political chatter point toward a victory by the Conservatives under David Cameron in the next election, to be held sometime within the next 15 months.

That's the good news for Cameron. The bad news is that he is being judged altogether differently today than he was even a few months ago. He's no longer just the leader of Her Majesty's Loyal Opposition; he's prime minister-in-waiting. Especially with the economy on the rocks, the public is paying closer attention to Cameron than it has in the past. They still seem to like what they see; polls consistently show the Tories leading Labour by 10 to 20 percent. But even Cameron's allies acknowledge he's got to raise his game. Leader of his party for just more than three years and an M.P. for less than eight, the 42-year-old is coming under increasing pressure to define himself and what a Cameron government would be like. True, policy papers continue to pile up on Conservatives.com, but Cameron remains appealing but frustratingly vague.

For a brief moment last year, it looked like Cameron's transition into power would be smooth. After a decade of Labour rule, political weariness had taken over, and Gordon Brown, lacking the panache of his predecessor, Tony Blair, looked doomed from the day he set foot in office. But when the public's unease about the economy turned to dread after the collapse of Lehman Brothers in September, the Tory leader seemed uncertain how to respond--hesitating, for example, about whether to support a government bailout of the banking system. This allowed Brown--the former chancellor of the Exchequer who presided over a decade of growth under Blair before succeeding him in 2007--to hammer away at the "do-nothing Conservatives." Suddenly Cameron looked like the indecisive "ditherer" he used to accuse Brown of being.

But slowly, as the financial meltdown worsened and questions began to arise about Brown's handling of the crisis, Cameron and crew sought to make up for lost ground. To match Brown's propensity for wonkishness, Cameron's conservatives took on "seriousness" and "experience" as their watchwords. To balance the perceived lighter-weight credentials of Cameron's friend and shadow chancellor, 37-year-old George Osborne, Cameron brought back as shadow business secretary the avuncular and popular Ken Clarke, a 68-year-old who had served in Margaret Thatcher and John Major's governments. Cameron promoted his respected and articulate shadow foreign secretary, former party leader William Hague, 47, making him his deputy "in all but name," as he put it. And Cameron's team moved beyond writing policy papers and into action. The shadow cabinet has begun meeting with senior civil servants to prepare a government changeover, and teams of consultants from KPMG and Deloitte, he says, have been "embedded in the process" of constructing what the M.P. calls "a 100-days-and-beyond plan. (He declined to disclose any specifics "so far ahead of the election.")

It's hard to avoid the comparisons to the last young politician to prepare to move into 10 Downing Street--Blair--and Cameron has done everything he can to invite them. In the early days of his leadership, Cameron would tell people privately that he, not Brown (whom the Conservatives loved to paint as an un-Blairite Old Labour retrograde), was the rightful "heir to Blair." But now that presumption--implying that ...