Everyone needs a Willie. Margaret Thatcher's trusted deputy may have appeared an amiable old buffer, but he was also irascible and "infinitely cunning". By Malcolm Rifkind

Splendid! Splendid!: the authorised biography of Willie Whitelaw Mark Garnett and Ian Aitken Jonathan Cape, 386pp, £20 ISBN 0224063111

''It is always better to be thought of as stupider than you really are than as cleverer than you really are." This remark, which ought to have been made by Willie Whitelaw, was in fact part of the wit and wisdom of Alec Douglas-Home. It should be no surprise that two of Britain's shrewdest and most successful politicians in the past 50 years built their careers on denigrating their own abilities and reminding us of their modest talents. It was not just good manners but reflected an awareness of the unusual, if not unique, nature of the British psyche.

In which other country would it be a damaging insult to be described, as Lord Salisbury said of Iain Macleod, as "too clever by half"? Is it conceivable that a French politician's career would suffer because he was thought to be too clever? Yet the British continue to worry about their politicians being too able, and God help them if they are intellectuals. Give us good, often inarticulate, statesmen like Willie Whitelaw and John Prescott, whose instincts are sound and who wear their faults on their sleeves, and we are comfortable.

The truth is, as ever, more complex, as the new biography of Whitelaw by Mark Garnett and Ian Aitken makes clear. The first puzzle, as this is an authorised biography, is why on earth Whitelaw asked Ian Aitken, whose political sympathies were light years to the left of his own, to be his official biographer. I look forward to Tony Benn inviting Simon Heffer or Bruce Anderson to be his. The consequence is not that the authors are unsympathetic or unfair to their subject. On the contrary, they could hardly be more friendly and the Whitelaw family should be more than content. But their political sympathies constantly intrude in observations and comments that are not relevant to a work of biography. Thus, in the chapters dealing with Whitelaw's years as Northern Ireland secretary, it is evident again and again that the authors are well disposed to the nationalist viewpoint and hostile to that of the Ulster Unionists.

Likewise, their personal distaste for Margaret Thatcher and for the achievements of her government is tangible. They are perfectly entitled to their views, but not when they are fulfilling the role of authorised biographers. It is Whitelaw's opinions we are interested in, and the authors' opinions of Whitelaw. The rest is self-indulgence.

Having got that off my chest, I can now be more complimen-tary to them. They bring out, very well, that behind Whitelaw's affable and amiable manner was a clever, calculating and impressive politician. One of the best descriptions of him was by one of his former civil servants, who referred to him as "that large, emotional, sometimes irascible, apparently spontaneous but infinitely cunning man".

He was a pretty impressive judge of people. In 1970, when Edward Heath was considering inviting Margaret Thatcher to join his cabinet, Whitelaw warned that "once she's there we'll never get rid of her". Whitelaw himself had no difficulty about getting rid of people. He was instrumental in ensuring that Michael Havers stepped down as Lord Chancellor; he blocked Lord Young becoming chairman of the Tory party; and I remember, vividly, the determination with which he got Nicholas Fairbairn sacked as solicitor general for Scotland after some fairly minor indiscretion.

But he was a reactive rather than an innovative minister, and it is doubtful whether he would have been able to excel at the top job. After he had retired, he explained why: "It isn't that I wouldn't have been ruthless enough about people. If I'd thought people weren't sufficiently up to the job I'd have been ruthless about sacking them. It's events where I wouldn't have been ruthless enough."

But the historic importance of Whitelaw was his relationship with Margaret Thatcher, and the crucial support he gave her in the difficult early years of her prime ministership, when she was cordially loathed by most of her cabinet colleagues. Every prime minister may not need a Willie, but she did. Whitelaw was being honest when he said that he had given up all leadership ambitions and intended to give her the support she needed. He was true to his word. She exasperated him; I don't suppose he liked her; he disagreed with most of the things she stood for. But, so far as we know, he never plotted against her, or gave any support to those who did. He recognised not only the support she enjoyed with the grass roots of the party, but that she had a remarkable ability to transform and revive the British people.

I joined the cabinet in 1986 and saw Whitelaw at the prime minister's side for the two years until he retired. On one occasion, I was in a minority of one in a cabinet committee discussion. At the end, I asked for my dissent to be recorded. This would have meant that the problem would have gone to full cabinet, with the possibility of a crisis clearly underlined. Whitelaw swung into action; I was made an offer that met my bottom line, and the crisis was averted. It was a classic example of both his authority and the soundness of his political instincts.

It would be highly desirable to have at least one Whitelaw in every British cabinet. Consider the advantage of a senior minister, no longer with personal ambition, able to tell the Prime Minister, without fear or favour, when he was acting foolishly, improperly, or in a manner that would do the government serious damage. That is the only justification for having a deputy prime minister; but there is as little prospect of John Prescott fulfilling that role in Tony Blair's cabinet, as Tariq Aziz in Saddam Hussein's.

But perhaps I am being unfair. As Willie Whitelaw once said, "I always feel it is quite wrong to prejudge the past". If you are puzzled as to the relevance of that remark to the previous paragraph of this review, then that is all to the good. Willie would have approved.

Malcolm Rifkind was foreign secretary from 1995-97