Here is the deal and why it is still not sealed. David Cameron has shown himself to be a highly proficient politician who has learned a great deal from Tony Blair about how to win against a tired, long-serving government. He is personable, clever and has done a good marketing job of changing perceptions of the Conservative brand.

He has even made a start at convincing us that his core values have changed from the old-school Toryism of his upbringing and the brittle Thatcherism of his youth. He has made a reasonable fist of arguing that, as the author of the 2005 Conservative manifesto, he was simply doing a presentation job on the right-wing programme of an older man, Michael Howard. He had his doubts, he would like us to know, even if he has to rely on what the Prime Minister would call the "props" of his family in order to persuade us.

It is argued plausibly on his behalf that the experience of raising his severely disabled son has changed his attitudes to the public services, and to the NHS in particular. And there is no doubt that his conversion to the cause of environmentalism is made more credible by his wife's former membership of Greenpeace. Yet the doubts remain, and over the past few months, while the financial crisis and the Labour leadership soap opera have dominated the news, it has felt as if Mr Cameron was allowing his party to snuggle back under its comfort blanket. Over the summer, he and George Osborne, his shadow chancellor who is interviewed by the IoS today, seem to have soft-pedalled on the "progressive" goals of the new Conservatism.

Mr Cameron has said, rightly, that we do not have to choose between economic growth and green objectives, but has not followed it up. The most notable recent stories have been "clarifying" an inheritance tax cut for couples worth £2m and a refusal to match future Labour spending that Tory activists have seized on enthusiastically as a promise of further tax cuts in the future. Above all, while the critique of New Labour has been sharp, the alternative policies have been fuzzy.

Our report today about the cloudiness of Conservative Party funding casts further doubts on Mr Cameron's conversion to a new way of doing politics. At the time of the Derek Conway business earlier this year, when the Tory MP was found to have put his son on the public payroll in return for no visible work, Mr Cameron ringingly declared: "Any arrangements we enter into are ones we are prepared to protect and defend in a court of public opinion."

To be fair, he showed some steel in forcing his reluctant MPs to publish details of family members they employed. But he has fallen short of the openness that he promised. The use of private clubs as a conduit for donations is an obvious loophole in the law that requires disclosure and that bans foreign money. Given the problems that Mr Blair had with funding, Mr Cameron should have acted before now.

As we reveal today, the Conservative Party under his leadership has received millions of pounds via unincorporated associations. We have no idea who the original donors are, or if they are on the electoral register in this country.

Our confidence in Mr Cameron is not strengthened by his continued evasiveness about the promises made by Lord Ashcroft, deputy chairman and one of the party's largest donors, who is personally funding Tory candidates in marginal seats. When Michael Ashcroft was raised to the peerage, he undertook to become resident in the UK for tax purposes, a question on which he now claims a right to privacy. Mr Cameron says that he accepts the assurances Lord Ashcroft has given him. This is not good enough for the rest of us. A candidate prime minister needs to do more to defend his party's funding in the "court of public opinion".

A believable commitment to clean up party funding is a precondition of gaining a hearing for a Conservative way of achieving the goals of social justice, civil liberty and environmental sustainability to which Mr Cameron now claims his party is dedicated.

The theme of Mr Cameron's message to his party on the eve of its annual conference is that it has not yet "sealed the deal" with the electorate. That is another way of putting this newspaper's unfashionable observation that all is not yet lost for Labour and Gordon Brown. The temptation in Birmingham this week will be for Tory activists to think that the fight for the allegiance of The Sun and the Daily Mail is all that matters, and that the right response to economic hard times is to cut taxes. With the election at most 20 months away, Mr Cameron has to tell them what they do not want to hear if he is to start to seal the deal with the wider electorate.