John Sergeant was always a somewhat underrated Westminster journalist. He eventually became the BBC's chief political correspondent but never its political editor, and it is only since his retirement (preceded by a surprisingly brief spell as political editor of the old ITN) that he has really come into his own. His 2001 bestseller, Give Me Ten Seconds, was a splendid piece of political knockabout and he has now produced an equally entertaining but more serious work, analysing the baleful influence that the last-but-one Conservative prime minister has had on the fortunes of her party.
The first part of the book, it has to be said, is pretty routine stuff. The author tells the familiar story of how the clouds gradually gathered around the 20th century's longest-serving prime minister, but there is little that is fresh or new. (Those who want a full account of Margaret Thatcher's fall still need to turn to Alan Watkins's A Conservative Coup, first published in 1991.) Where Sergeant does break new ground is in establishing the impact that the words and deeds of the fallen leader have had on the party, right from that grim moment in November 1990 when the ballot of Tory MPs (That-cher 204, Heseltine 152) was declared. Inevitably, that result led to her reluctant abdication within 48 hours.
Sergeant's indictment is a powerful one but, like all the best advocates, he is ultimately dependent on his witnesses - and it is they who do the real damage. He even explains how the seed for the theme of his book was planted by none other than the former Tory party chairman Chris Patten. Bumping into him at a social gathering, Sergeant happened to explain that he was writing a book about Margaret Thatcher. "Oh yes," the last Tory chairman to win an election cheerfully replied, "she des-troyed the Conservative Party."
And this, according to Sergeant, is exactly what the most dominant politician of the second half of the 20th century ended up doing. From her determination not to be succeeded by Michael Heseltine, through her increasingly disloyal behaviour to her successor John Major, to her relentless insistence on getting first William Hague and then Iain Duncan Smith elected in place of the far more formidable Ken Clarke, Thatcher's legacy to the Conservatives has been wholly destructive. In advancing this case, Sergeant does not need to unearth new facts: it is enough that he recites the record, and he does so to devastating effect.
Even by the time Thatcher retired, her party was already impaled on the hook of Europe. But instead of treating the issue warily - it had, after all, been no less res-ponsible than the poll tax for her eviction from No 10 - she insisted on scratching at it and inflaming it until it looked more like a running sore than an ancient scab.
To be fair (and, despite his views, Sergeant always tries to be that), this book does enter a plea in mitigation. The Whitehall machine, the author goes out of his way to point out, consistently did its best to keep Thatcher's wilder flights of fancy under control. She might occasionally go off on a "bender", as with her passionately anti-European Bruges speech of 1988, but on more mundane issues the machine and the mandarins for the most part contrived to keep her on the straight and narrow.
Suddenly, though, from December 1990 onwards, all the mechanism for containing excess deserted her. Established in London at her grand mansion in Chesham Place, Belgravia - HQ of the increasingly purposeless Thatcher Foundation - she acted like the representative of some sovereign, independent power, beholden to no one and more than capable of formulating her own policies regardless of the consequences. It was this kind of irresponsible conduct that prompted Ted Heath to murmur, when asked to explain it: "I don't know. I'm not a doctor."
Sergeant's dark, Miss Havisham-style portrait is made all the more authentic by the obvious awe in which he once held his subject. There is a vivid vignette at the end when he spots the former "Leaderene", almost restored to her full glory, at one of last summer's royal garden parties. He does not dare approach her - she, unlike virtually all those who were her colleagues, has refused to be interviewed - so he simply gazes upon her, "as you might on a former film star". Make that Bette Davis, and I guess we can all identify with his feelings.
Anthony Howard's Basil Hume: the monk cardinal will be published by Headline in June