It was like a gay wedding. The only problem was that one of the partners, David Cameron, walked out of the service after about five minutes. He had only just walked up the aisle with Phillip Blond, the self-styled "Red Tory" dubbed his "philosopher-king," to launch Mr Blond's new think-tank ResPublica.

Mr Cameron's departure, after some brief remarks about his commitment to "progressive conservatism", surprised the 300 guests, who included many of the best brains in the political and think-tank world. His exit was symbolic. He wanted to be seen to be associated with fresh thinking from outside the usual Tory box – but not too associated. So he pleaded a busy diary and did not stay to be asked questions about which of Mr Blond's ideas he agreed with. Breaking up the supermarkets and other cartels? A dangerous path. Repudiating Thatcherism as uncaring? Tricky for the leader of a party which still reveres her. So Mr Cameron found a third way: being there and then not being there.

As I waited for the ceremony to begin, I couldn't help thinking I had been here before. Neil Kinnock and Roy Hattersley once arrived arm in arm to launch Labour's manifesto but my recollection was much more recent than that. Then I remembered: Cameron and Blond had launched a "progressive conservatism" project at the think-tank Demos in January.

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Mr Blond departed abruptly and has now started his own think-tank, with plenty of money rolling in as the political tide appears to shift in the Tories' favour. No one is talking about why he fell out with Demos. I am told there were "political and philosophical differences" over the agenda Mr Blond wanted to pursue. Demos, while priding itself on being free-thinking, wanted to keep its liberal principles. So perhaps that tells us something about Mr Blond.

Closer examination confirms that he has less in common with Mr Cameron than the well-orchestrated hype around the launch of ResPublica suggests. Mr Blond is a bit of a lefty on the economy but conservative on social issues like homosexuality and abortion. In contrast, Mr Cameron is socially liberal but economically conservative: the global recession forced him to make a big choice and he opted for fiscal conservatism, dropping the Tories' pledge to match Labour's spending plans and calling for faster, deeper cuts in the public deficit. Labour folk suspect that it suits Mr Cameron to flirt with his "Red Tory" friend, claiming it is part of his drive to distract attention from his return to a Thatcherite economic agenda of big public spending cuts.

The Tory leader has alighted on one of Mr Blond's themes, that "big government" has helped to create a "broken society", while conveniently ignoring the fact that he also blames free markets and liberal morality. There's nothing wrong with party leaders adopting a "pick and mix" approach – they always do – and Mr Blond may have an important role to play in putting some flesh on the rather bare bones of the Tories' localism agenda and the bigger role they envisage for voluntary groups and social enterprises.

His mission statement says: "ResPublica will outline a clear path towards a renewed civic society through realising the common goals of mutual responsibility, sustainability and achieved wealth by all." No one would argue with that. The challenge is to convert it into hard policy. Kenneth Clarke, the shadow Business Secretary, is said to be sniffy about Mr Blond's ideas for reining in the market and I wouldn't expect too many of them to find their way into the Tory manifesto.

Indeed, Mr Blond's influence has been overstated. He is not, as he has been described, a close adviser, speechwriter, guru, favourite thinker or philosopher-king for Mr Cameron, not least because the Tory leader has already got one in Steve Hilton, the former ad man who has long been preaching the need for a responsible capitalism.

Think-tanks play an important role in politics. But they have their limits. Policy Exchange enjoyed the title of Mr Cameron's "favourite think-tank". Until, that is, it issued a report suggesting that places like Liverpool, Bradford and Sunderland were beyond saving and that the locals should move south. Ideas like that were hardly going to help Mr Cameron's drive to win friends – and seats – in the north, and he felt moved to condemn the idea as "insane."

Other proposals have been more productive. The Institute for Public Policy Research (tax and benefits reform, the London congestion charge) and the Labour-affiliated Fabian Society (the earmarked tax rise for the National Health Service in 2002) produced some ground-breaking ideas for New Labour. Today even the left-leaning ones, needing to raise precious funds in a competitive market, cuddle up to the Tories. Demos will soon produce an important report fleshing out Mr Cameron's plan for 16-year-olds to do national citizen's service. It may fare better than some of Mr Blond's rather more philosophical ideas.

Indeed, some senior Tories suspect that ResPublica may have been born a little too late in the electoral cycle to be able to turn Mr Blond's thinking into fully costed, workable policies fit for the difficult economic times in which a Tory government would take over. As one put it: "We don't need philosophy and fluff; what we need is some crunchy policies."