Steve Richards: PM's big idea is still alive – but is it really that big?

The relationship between political leaders and big ideas is similar to that in a film noir when the hero falls for the femme fatale. The hero needs her, even though she will lure him into danger. Leaders also need big ideas and yet often they are scared of them.

David Cameron's self-proclaimed big idea is the Big Society. From the beginning it has been hailed, mocked, attacked, imitated and been the subject of internal agonising. Even now there is speculation that it is being cast aside as his entourage in No 10 seek clearer definition around the economy and fairness, the more accessible themes of the Prime Minister's New Year's message. There the Big Society was cited in its vaguest manifestation yet, as an umbrella term to describe all that the Government planned to do in the coming year.

No 10 is adamant that neither the idea nor the term is being marginalised, let alone dropped, pointing out that today Cameron presents his 2012 Big Society Awards and will be making another speech on the theme soon. But its more passionate advocates – and some of his closest political friends remain fervently committed – are concerned that it is becoming a big idea which describes every policy from fairness at the top and bottom to infrastructure projects.

For a new series for BBC Radio 4, I describe the bumpy ride of Cameron's big idea, which he has described as his political mission, from its origins to the current internal questioning about its centrality. What is striking is not the irrelevance of the idea, but the degree to which it has shaped Cameron's leadership from the beginning. In his victory speech, his first as Conservative leader, Cameron declared that there was such a thing as society, but it was not the same as the state. After several failed attempts at a snappier definition, this clever, multi-layered phrase evolved into the Big Society.

Cameron's friend, Danny Kruger, who worked for him in his early days as leader, told me: "I know that David Cameron is in office to enact or see happen or help to grow the Big Society. That's his driving mission... if he can do anything by the time he leaves office, it'll be to see a bigger, stronger society." He is convinced the Prime Minister will never let go of it.

On one level he has never done so. It was the theme of the Conservatives' entire election manifesto in 2010, a populist booklet on the supposed empowerment of people. At a series of pre-election seminars attended by Shadow Cabinet members, Cameron described the redistribution of power as the Conservatives' big idea, a theme that played an underestimated role in the formation of the Coalition. In the series, the Liberal Democrat Chief Secretary to the Treasury, Danny Alexander, describes the negotiations over the Big Society as "the most interesting and illuminating, because they revealed not just differences, but also real synergies in terms of policies... I was enthused and encouraged by that part of the discussion because none of us around the table knew each other... but particularly in the area of localism and the need to decentralise power, though there are differences... there's an awful lot of common ground there too and it was exciting to see an agenda for government develop that really could change the way the country worked".

Alexander has a point. From the Localism Bill to the NHS reforms a legislative programme is being rushed through with what Vince Cable described as an almost Maoist determination. So why do so many doubts persist inside the Conservative party?

Part of the problem has echoes with Tony Blair's Third Way. Blair emphatically recognised the need for a big idea but was frightened by the consequences if it was too clearly defined. The Big Society has already had much more practical impact than the Third Way, but it is still vague enough to stand both for small incremental change or a near revolution. In the series, Kruger sees its origins under the leadership of Iain Duncan Smith and describes himself as having a right-wing view of the Big Society. David Willetts traces its roots further back to his advocacy of civic conservatism in the 1990s.

Some contributors are adamant the size of the state is not part of the argument and point out rightly that it was formed when Cameron was still committed to Labour's spending plans. Others insist that Cameron had always planned to shrink the state. One tells me privately that the project is "reheated Thatcherism". Others regard it as "Blairite". Some suggest Cameron regards his idea mainly as local volunteering. Others think it includes sweeping public service reforms.

Some of Cameron's closest supporters, reflecting the views of Steve Hilton from within No 10, regard the stalling of the NHS reforms as the moment when their big idea was in mortal danger. More modestly some cite the community group, London Citizens, as its model, the forum where Cameron's senior adviser Rohan Silva met and came to respect Blue Labour's Maurice Glasman. At first Glasman was an alarmed admirer of the Big Society.

Blair's Third Way was impossible to define. Cameron's risks too many definitions. Its imprecision collides with another familiar factor in relation to Prime Ministerial big ideas: tensions with the Treasury. Privately Cameron has been known to reflect, at least early in power, that there were more internal differences with the Treasury as an institution than with some Lib Dems. Tactically George Osborne's allies tell me they regard it as a mistake to have fought the election on the Big Society. Cameron's friend, Ian Birrell, insists they are wrong and traces their pre-election drop in support to their more austere economic message. In terms of substance, the Treasury wants to know that every penny of public spending is well spent. Under the Big Society, that is impossible.

Above all, big ideas involve risk taking. But Cameron has noted enviously how in polls voters placed Blair precisely on the centre ground. Blair clung there partly by having a big idea so vague that even when he made his most ideological speech attacking the "forces of conservatism" he could not agree with his advisers what those forces were. There is a brilliant account of the panic-stricken build-up to that 1999 conference speech in Alastair Campbell's diaries. Cameron should read it. So should Ed Miliband's internal critics. Big ideas are dangerous, but not as dangerous as not having any.

The first episode of David Cameron's Big Idea by Steve Richards is on Radio 4 this Sunday at 1.30pm, after The World This Weekend, and also on the BBC iPlayer

s.richards@independent.co.uk; twitter.com/steverichards14