So how did Oliver Letwin — though an arch Thatcherite, though an architect of the poll tax — think his way round to being the arch moderniser?
Finkelstein comes to praise the wizardry with which Letwin as the Tory Gandalf has moved the argument on from Thatcherism, without ever repudiating it.
This reflects the "electric fence" set around the modernising project. In a piece for the Fabian Review, I suggest that those boundaries around Cameron's Tory modernisation were set a decade ago, the last time the party almost began a substantive debate about whether it wanted to remain Thatcherite or not.
Yet the spectre of Thatcherism has haunted Tory modernisation for rather longer. Before the Conservatives decided that they did not need a "Clause Four" moment, they did try to have one. The limits of Tory modernization were set a decade ago, in April 1999, when deputy leader Peter Lilley tried to lay the Thatcherite ghost and failed.
Lilley’s R.A. Butler lecture now reads like a litany of mild Cameronite truisms, primarily that the party would never be trusted on public services if voters believed they were essentially hostile to a publicly funded welfare state. Lilley seemed to have the right Thatcherite credentials to mildly suggest not any form of apology, but that the party should stop “glorying in past successes” or “refighting battles” it had now won.
Yet all hell broke out. Party reaction at every level was “overwhelmingly negative”, as Tim Bale details in his excellent new book The Conservative Party from Thatcher to Cameron. Among the most vituperative voices was Michael Gove, later to become a leading moderniser. Gove wrote that “no location is as undignified as being ‘in the centre’, where the lowest common denominator and the highest public spending meet ... an arid region where no principles can take root … a particularly shameless place for politicians to be”. For Gove, government could never spend better than “freer citizens liberated by a smaller state”.
This had two long-term effects. That it delayed any Tory rethink until two more defeats is well known. Less noticed is that the neuralgic reaction to Lilley set an electric fence to demarcate the limits of Tory modernisation: no Conservative frontbencher has offered any substantive critical assessment of the Thatcher legacy since.
So Cameronism has been primarily an often successful exercise in "brand decontamination". Every means of modern political communications was central to the project. What was off limits was any substantive or contentful critique of the party's recent past or its deeper ideological commitments.
By contrast with New Labour, which created the sharpest of breaks with the party’s history in its caricature of “Old Labour”, the ProgCons have had no account of their recent history at all. This also cuts them off from reclaiming the party’s pre-Thatcher political and intellectual traditions which thoughtful modernizers like David Willetts wish to revive.
After all, Keith Joseph and Margaret Thatcher could hardly have been clearer about the scale of the rupture the New Right would make with soggy, consensus Conservativism of the post-war period. "Before 1974, I had not been a Conservative at all", as Joseph famously wrote.
As ConservativeHome's candidate and activist surveys regularly show, this remains a major issue of party management. As Finkelstein notes, much of the party remains committed to Thatcherism; the public wants to know the party has changed.
Hence the need for Letwin's wizardry. Letwin squares that circle by arguing that what has changed is the context.
This allows Letwin to refuse to say in public where or whether Cameronism differs substantively from Thatcherism, arguing that the question is meaningless: “Are you a Thatcherite now is a meaningless question", he told me at the Demos progressive Conservatism launch a year ago. Letwin does now argue that inequality matters, and says he is now philosophically agnostic about whether the state should be larger or smaller. Yet applying that (New Labour) "what works" test brings him back to Thatcherite means after all, since he thinks the empirical evidence is for a smaller state.
This leaves David Cameron arguing that "the party has changed" without being prepared to identify - beyond diversity of personnel - what that "change" is.
So I still think this lack of any substantive account of Thatcherism cuts progressive Conservatism off from its pre-Thatcherite intellectual and political roots, or from an engagement with the causes of the social problems - notably inequality and the broken society - that the big society agenda seeks to challenge.
An imaginative but not wholly persuasive approach to this problem was offered by David Willetts in a major Prospect article on the 30th anniversary, in which he made the counter-intuitive argument that Thatcher and Keith Joseph had been wrong to argue they were offering a major rupture with post-war Conservatism, and were as much about continuity as change.
It is striking, after three decades, just how carefully the most modernising voices in the Tory party must tread around the Thatcher legacy. Certainly, none has forgotten the Lilley row of 1999 or has shown any appetite to reopen that argument.