When 32 floating voters were asked who they rated most after watching clips of Tony Blair, Gordon Brown, David Cameron and Sir Menzies Campbell, most hands went up for Mr Cameron. But a hesitant woman cried out: "If he wasn't a Conservative."
It was a revealing moment. People like Mr Cameron but remain very unsure about his party. Frank Luntz, the former US Republican Party pollster who conducted the fascinating group discussion for BBC2's Newsnight programme, concluded: "David Cameron was the winner. But they still question whether or not he will deliver and, more importantly, [whether he] represents the Conservative Party or is alone in the Conservative Party."
The Tories may have a young, red-hot salesman but the brand remains tarnished. Their advisers believe this explains why, for all the Government's problems, the Tories are not five points ahead in the opinion polls rather than trailing Labour. Even in an era of presidential politics, people vote for a party as well as a leader.
Mr Cameron knows he needs to transform his entire party. According to an ICM poll, six out of 10 people believe he is a "new face" but that his party has not really changed much. Even 48 per cent of Tory supporters share that view. Forty per cent of voters agree that Mr Cameron's leadership was "more about spin than substance", while 29 per cent disagree.
This week Mr Cameron tried to answer the criticism by ensuringthe spectacular photographs and television footage from his visit to an Arctic glacier to see the effects of global warming were underpinned by some fresh thinking on how the Tories would tackle the problem.
Even then, a Populus survey for the BBC's Daily Politics show found that 62 per cent of people believe he is "only talking about the environment because he thinks it will make people more positive about the Conservative Party, not because he really cares about it". Public scepticism about politicians is turning into cynicism. Although Mr Blair is partly responsible, it harms Mr Cameron too.
The Tories' policy review teams will not report until next year and they cannot afford to have a policy vaccum until then. After a strong start, Mr Cameron's novelty to the media has worn off. He has hit a plateau, and needs to find some booster rockets.
Labour has taken its time to decide how to attack Mr Cameron but is now turning its guns on him. When I went to the launch of Labour's election broadcast depicting the Tory leader as "Dave the Chameleon", who changes his colour and message to suit his audience, my first thought was that it was a classic case of the pot calling the kettle black.
Mr Blair was nothing if not a chameleon after becoming Labour leader in 1994 - and a very successful one at that. If the Daily Mail wanted a headline about him promising to be tough on crime or benefit scroungers, he would happily provide it. In The Sun, he was the man who loved the pound, even though he privately hoped to get rid of it. Never mind.
This week's Labour's broadcast didn't say anything about Labour and yet I suspect the party is on to something with its attack on Chameleon Cameron. Ploughing through a pile of newspaper cuttings the other day, I noticed that Mr Cameron was warming to a "cuddly on crime" policy being advocated by his home affairs spokesman Edward Garnier, which would mean, in effect, tearing up the "prison works" mantra of Mr Cameron's mentor, Michael Howard.
The only trouble was that, two days later, the News of the World ran a headline screaming "I'll call time on lags" after Mr Cameron told the newspaper: "It's ridiculous the way people are let out before their sentences are complete ... Prison will not be a deterrent until people serve the sentence they are given by the courts." Memo to Mr Cameron: don't send conflicting signals.
When Newsnight's focus group was asked what it wanted, there was a one-word chorus: "change". No wonder Mr Cameron bangs on about it. There was an almost unanimous demand for one particular change - for Mr Blair to stand down sooner rather than later. Watching Blairites would have been pretty depressed - the participants have lost faith in Mr Blair and there is nothing he can do now to win them back.
What sort of change do people want? They will essentially be offered two options at the next election - a Tory government or an extended tenure for Prime Minister Brown. The focus group was much more positive towards Mr Brown than to Mr Blair, although it liked Mr Cameron more.
It may be unfair, but looks matter: Sir Menzies scored badly because he was judged "old", even though the focus groupies liked Liberal Democrat policies. Of course, the participants were judging the Chancellor as they see him now. I suspect he will look very different as Prime Minister. How he looks then will be one of the two most critical question in British politics and no one knows the answer now.
The other question? Whether the public believe the Tories have really changed and not undergone what Peter Mandelson recently called a "spray job". He was drawing a distinction between Labour's necessary but inadequate policy shifts under Neil Kinnock and the more substantial ones under Mr Blair, which finally persuaded the voters the party had changed. Mr Cameron's daunting task is to complete the transformation which took Labour 14 years in less than four. He has a mountain as well as a glacier to climb.Reuse content