In the dying days of James Callaghan's regime, the command went out from Caesar Augustus (via the Cabinet Secretary) to senior mandarins: don't talk to Peter Hennessy. This had, predictably, the reverse effect, helping the author to build up his network of Whitehall relationships, on which he has drawn to paint uniquely knowledgeable portraits of modern government. Hennessy has tackled our overgrown, uncodified system with the infectious enthusiasm of a Charlie Dimmock, digging into heavy clay to expose "the hidden wiring". In this excellent book, however, he half-turns from process to personality, writing about the "First XI" who have held the post since 1945.
His clear favourite is a man with "all the presence of a gerbil". Clement Attlee is the only one of the 11 to appear on both of the author's award lists: one for impact (along with Margaret Thatcher, less gerbil than tigress) and the other for niceness (with Alec Douglas-Home and John Major). Winston Churchill's war years are outside Hennessy's frame; he concludes merely that "the Cabinet Room seemed a smaller place" when Churchill left, and has remained so ever since.
Anthony Eden takes the wooden spoon, the author agreeing with Noel Coward that he was "a tragic figure cast in a star part well above his capabilities". It is the two Harolds - Macmillan and Wilson - whom Hennessy finds most difficult to place in his premier league: both experienced, wary, masters of the media. He labels both as a "moderniser", but neither, in the final analysis, was able to do more than identify the growing list of seemingly intractable problems.
Ted Heath he marks up as a "scene-shifter", along with Tony Blair. But these come a big step below the weather-makers: Attlee and Thatcher. Attlee, the author acknowledges, was the inheritor of a vast change in the weather brought about by the Second World War. Thatcher - elected, so she believed, "to change the facts" - made her own weather.
But it is the sharp tastes of the different premierships, not the final scores, that make this book. Here is Macmillan, who "regarded himself as a practical person, a businessman as well as a swordsman and a gownsman", brought low by the pain of his prostate trouble, provoking his colleagues into typical behaviour when he asked them if he should carry on. ("They all concurred with the exception of Enoch Powell; Lord Hailsham wept; Rab Butler offered him a Valium.") Here is Harold Wilson blotting out his BBC interrogator, buying time for thought and distracting the viewer while lighting up, before the election in which the "man with the pipe" surprised everyone by losing to the "man with the boat". And here is Tony Blair, getting through Cabinet meetings on first-name terms, in a brisk half-hour, and operating (as Jack Straw puts it) as chief executive with a number of subsidiary companies.
All the same, we are given much more than vivid anecdotes; this is quite simply the best analysis yet of the modern practice of prime ministership. How curious it is that Attlee should have emerged as top deity in the modern Labour pantheon, when he so disapproved of the "excessive prime ministerialism" that Hennessy detects in the Blair arrangements. Not that Attlee was a weak man; he was the best butcher of the lot, dismissing ministers much more briskly than the Iron Lady. As he said: "Democracy means government by discussion, but it is only effective if you can stop people talking."
Attlee, however, had modest views on the issue of prime ministerial overload; he considered that the time he gained from living on the job, rather than driving in from Stanmore, amply compensated for the extra work. No modern prime minister would take the same view. Whether today's prime minister works harder than Gladstone is more of a question: he, after all, spent hours in the Commons, taking through bills himself, through the night, if necessary. While the bemused press were still contemplating his huge majority, Blair managed to cut down his parliamentary question time to once a week.
I have only two mild criticisms. The first is that Hennessy does not, perhaps, give enough credit to Thatcher's successor for bedding down her revolution into consensus. The second is just a question. A thoroughly likeable man himself, Hennessy clearly cannot help liking both politicians and officials, and this generosity of spirit informs and enhances his book. However, to an extent he perhaps does not realise, awe is reserved for two civil servants: Norman Brook and Burke Trend. Yet surely someone who understands so well the terrible trade of politics should, in the end, rate the risk-takers above the mandarins? Politicians who expose themselves to "the inevitability of disappointment", who offer up their reserves of self-belief to the brutal depletions of public life, may be stupider, weaker, more eccentric and erratic than the mandarins. But are they not also more courageous?
Sarah Hogg was head of the Downing Street Policy Unit (1990-95)