As the longest-serving prime minister of the 20th century, as the only party leader to win three successive general elections in that century, and as the first woman to lead a major political party, Margaret Thatcher's place in the pantheon of British history is assured. But what will that place be, and what is her current reputation? After all, as a self-confessed radical who, in her own words, set out to "change everything" and did so according to detractors and devotees alike, hers was a party leadership and premiership steeped in controversy. Forged in the crisis of the Heath Government's collapse and ending abruptly 16 years later, not with defeat in a general election but because of the results of a rather different ballot box - the one employed by a group that likes to call itself the most sophisticated electorate in the world - the Thatcher years are critical for the Conservatives and for Britain. But just how critical, and to what extent was Thatcher as much a creature of her time as the creator of her time?

Few are as well qualified to provide an assessment of Thatcher and Thatcherism as Ewen Green, who for 20 years or more has been examining forensically - to quote the title of an earlier collection of his essays - the Ideologies of Conservatism . In that work he explored how the Conservatives, often proud in principle and in practice of J. S. Mill's description of them as "by the law of their existence the stupidest party", generated and employed ideology to underpin their 20th-century electoral hegemony.

However, being the governing party for nearly three quarters of that century was as much to do with the electoral system and the fractured nature of the opposition as the positive appeal of the Conservatives. For example, in no election since 1945 has the ratio of the progressive vote share (Labour plus the Liberals, now the Liberal Democrats) to the Conservative vote share ever fallen below par (it has averaged 1.4 : 1) while the Conservative vote share has been falling at every general election in which they secured power since 1955. They were massively defeated in 1906, 1945 and 1997, and the truth of modern British politics is less that "Britain is a Conservative country that occasionally votes Labour" (as the party's unofficial historian, John Ramsden, claimed shortly after the 1997 defeat) than that Britain is a conservative country that prefers not to vote Conservative unless the principal progressive alternative is not so much progressive as extreme.

In one of the most interesting of the chapters in his earlier collection, Green explored the historical roots of Thatcherism, showing how Thatcher's rise to power was grounded in grassroots Tory scepticism about the Keynes-Beveridge-managed economy-welfare state. So much so that she was regarded - and to judge from the five leaders since 1990 is still regarded - as the only Conservative leader who has ever actually shared their beliefs.

ÁñÁ«ÊÓƵ

Building on this foundation, in this new study Green has three ambitions: first, to separate Thatcher from Thatcherism, thereby contextualising both; second, to demonstrate the long-standing (and largely consistent) basis of Thatcher's political philosophy and her position on most policy issues; and, third, to carry forward his broader project on Conservative political thought and the meaning of Conservatism through an exploration of what he calls the Conservative subculture, that of the grass roots and back benches, who until Thatcher were heard but largely unheeded in the Conservative conversation from which policy emerges.

It is important to stress that this is not a biography but an exploration of Thatcher's political, public reputation as it evolved from her entry into the subculture of Conservative politics in the mid-1940s (she was not elected to Parliament until 1959) through to her position as an elder stateswoman in the early 21st century, including her last book Statecraft (2002) where, according to her critics, her little Englander Euroscepticism finds fullest expression.

ÁñÁ«ÊÓƵ

Inevitably, and rightly, Green's Thatcher will be read alongside the only two Thatcher biographies that improve our historical understanding: Hugo Young's aptly entitled One of Us and the more recent two-volume life by John Campbell, Margaret Thatcher . Equally, it will serve as an all-important counterweight to the deeply flawed autobiographical apologias of Thatcher and her first two chancellors (the so-called biography wars of 1992-94), upon which too many analyses of the 1970s and 1980s have necessarily been dependent. That Green and others are now mining the Conservative Party archives, the Thatcher papers and the CD-Rom of Thatcher's complete public statements compiled by Christopher Collins, allows at last an escape from Thatcherite hagiography.

The first fruits of archive-based revisionism are evident in Green's assessment of 1975-79, a critical period for policy formulation and evolving political strategy as Thatcher, Keith Joseph and others prepared the ground for what would become the longest period of continuous Conservative government in the 20th century.

The assessment of Thatcher and Thatcherism is pursued through six substantive chapters that explore the main policy areas and themes that defined her premiership and form the focus for debates about legacy and reputation.

The first concerns the economy, a natural starting point given that from the outset of her party leadership Thatcher conceived of the next general election as "our last chance to rescue the British economy from the depressing spiral of decline". Green judges the subsequent record on the performance and governance of the British economy as somewhat mixed, but this is inevitable when the terminal date is taken as 1990 and supply-side policies, then at an early stage, have long-term paybacks. He is equally sceptical about the second policy area, privatisation, where he deftly weaves the economic with the political case for what was the biggest transfer of resources since the dissolution of the monasteries.

ÁñÁ«ÊÓƵ

On the third theme - trade unions - Green is much more positive about the significance of the changes wrought between the winter of discontent and the sea of comparative tranquillity that comprised British industrial relations by the 1990s. Interestingly, his account of Thatcher's motives for reform is much more than a story of political revenge and of governance reform to remedy the economic problem of trade unions and as much about Thatcher's organicist conception of society and of the appropriate place of voluntary, civil organisations.

The fourth theme is Thatcher and the electorate, and Green confirms her reputation as a highly strategic politician who pursued populist themes to attract voters. There is also interesting new material here on her nemesis, the poll tax. Green shows that it was a long-standing Conservative dream to reconnect local voters and taxpayers.

Two chapters relating to foreign policy then complete the analysis, with one on Europe and the other on the rest of the world, which tests the emerging themes against the topics of the Cold War, the birth of Zimbabwe, South Africa and the Falklands. Thatcher's comparative inexperience in foreign affairs in 1975, even 1979, is well known, but Green here explores why throughout her career she almost invariably defined international affairs in Manichean terms, a polarity that might allow short-term gains (the EEC budget rebate) but at the expense of longer-term developments that were not to her taste, and most spectacularly so in relation to how in her enthusiasm for the single European market of the 1980s she did not seem to appreciate until too late that there was an underlying momentum for European monetary integration. This, of course, resonates with the central strand of the current historiography about Thatcher and her eponymous incarnation, that which stresses the many ironies and paradoxes of her premiership and legacy for her party and, apparently her greatest creation, that of new Labour.

Roger Middleton is professor of the history of political economy, Bristol University.

ÁñÁ«ÊÓƵ