Opinion pollsters are fond of rating the judgement, arrogance, understanding, capability, flexibility, honesty, personality, experience, narrow-mindedness, common touch and patriotism of our leaders.
A rather more important question is missing. Though there is frequent discussion and debate about the intellectual roots and resources of our leaders, even about their place in the historic pantheon, there is a curious British diffidence, even embarrassment, when it comes to the question of intelligence.
Naked ambition, native cunning, killer instincts, the manipulative skills of a masseur, the ability to communicate and inspire, even a degree of cleverness, are necessary qualifications in any prime minister. Intelligence is more than the sum of those parts. It is essential not only to be able to think and analyse, plot and plan, but also to apply the strategic analysis to best effect. Delivery is every bit as important as direction.
Tony Blair has many faults, not least the ruthless, blinkered dedication he devotes to the task in hand. But I believe he is the most intelligent prime minister we have had since the second world war, because he knows where he wants to go, decides how to get there, and then does it.
The breadth and depth of his approach to problems, together with the range and detail of his activity, is tremendous. From wars to ways of cracking the blockages between the NHS and the patient, the locking out or locking up of burglars and the intricate dance-steps of the Northern Ireland peace talks, nothing is above, beneath or beyond Blair. He is obsessive: he niggles and meddles and looks over the shoulders of his most senior colleagues. The discipline of his approach completely justifies the charge of control freak.
Where some leaders trust their colleagues and let them get on with it, Blair will be on the shop floor, jacket off, goggles on. He will be slaving over a hot lathe before his colleagues have even clocked on. Only when he has shown ministers precisely what he wants, and how it should be done, will he leave them to it. There is very little trust involved.
No prime minister is an island. As Attlee had Bevin, and, to a lesser extent, Thatcher had Whitelaw, Blair has Gordon Brown, with whom he shares the burden. He has also leant quite heavily on Peter Mandelson over the years, tapping into his strategic advice. His calculation, and it is calculation more than gratitude, is that Mandelson's wheeler-dealer qualities make a real contribution.
The methods are pragmatic: thought, calculation, ruthlessness are all geared to delivery. But they are the means to an end, and Blair's ends are entirely principled: social justice, quality public service, equality of opportunity and a reassertion that citizens have responsibilities as well as rights. He refuses to accept received wisdom about how to achieve those ends. "He approaches these things with a blank piece of paper," a very close colleague says.
Blair deals with problems ignored and ducked by others over many decades. When he became leader, he knew that he first had to tackle the Labour Party itself. He had already decided to bury public ownership, the union ties and the power of the loony left. The rewriting of Clause Four, the search for alternative sources of party funding - some of which might be embarrassing - and the breaking of activist power in the constituencies and at party conference were part of the delivery.
Here, as subsequently in government, Blair knew where he wanted to go but did not always reveal the destination. If the end is difficult - as it would be with the gradual injection of private provision into the NHS in particular, or the welfare state in general - he will not leave it exposed to attack.
Blair's stealth has purpose; you do not climb mountains in straight lines. But mountains have indeed been climbed: economic stability; successful, working alliances in Europe as well as Washington; Northern Ireland; the national minimum wage; and starts on tackling long-term unemployment and the poverty trap. The foothills, often as difficult, have also been occupied: devolution; the hereditary peers; and freedom of information. Nothing is ever perfect. For example, Lords reform is unaccompanied by election; freedom of information comes neither with will nor means. But think of how Blair has made a start on tackling issues - such as social exclusion and sink estates - that governments of every hue have shamefully allowed to suppurate for 40 or 50 years. Rather than bulldozing the sink estates - a sort of blanket bombing - and then building again, Blair has introduced a patchwork policy that stitches together employment and crime, education and health, housing and homelessness, the poverty trap, anti-social behaviour and teenage pregnancy. Blair calls it joined-up government, and if something gets results, he wants best practice spread to best effect.
No wonder his Labour opponents hate him so. Roy Hattersley is entirely right when he says that Blair is obsessed with government and has little interest in politics. If politics gets in his way, Blair has no qualms about neutering the nuisance. "We will be a radical government," he wrote in the manifesto. "But the definition of radicalism will not be that of doctrine, whether of left or right, but of achievement . . . What counts is what works."
He has "modernised" Labour; now he plans to "modernise" Britain. In his own words, "this means knowing where we want to go", but not necessarily, one might add, giving a map reference; "being clear-headed about the country's future", but not always being as clear in spelling it out; "telling the truth", but not always the whole truth, if it defeats the purpose of the exercise; "making tough choices", but not all at once, if salami-slicing is more effective.
The result, to many, may look like aimless flailing in the dark, with procrastination on transport, the shenanigans over the London mayor, the painfully slow process of Lords reform and so on. But Blair doesn't mind taking the occasional step backwards. It is often the only intelligent response to an intractable problem. Faced with an immovable obstacle, Blair will go round it and return later. He is very good at biding his time. If history shows where mistakes were made, he tends to learn from them, rather than repeat them. IRA disarmament is called decommissioning and stalled, or parked, while the process creeps forward; if the Lords can be reformed only by chucking them the sop of 92 hereditary peers, so be it.
Yet sometimes Blair's stated aims can seem impossibly ambitious. At Labour's conference in Bournemouth last autumn, he not only promised to end child poverty, but also said that Labour's historic mission was "to liberate Britain from the old class divisions, old structures, old prejudices, old ways of working and of doing things, that will not do in this world of change". Peter Hennessy, professor of contemporary history at London University's Queen Mary and Westfield College, argues that "the gods will be laughing at that; the declarations on poverty and class and also taking on the forces of conservatism are a bit ludicrous". But Blair was and is serious.
So how justifiable is my claim that he is the most intelligent postwar prime minister? The awfulness of Major, Callaghan, Home and Eden is evident enough. Churchill and Wilson were well past their best in their replays. Macmillan had a strategic sense of history, but he was too laid back, too fond of Jane Austen and paid the penalty in the manner of his going. Thrown by the economy, thwarted by de Gaulle, he left country and party in an abject mess. Wilson in his first term, for all his cleverness, was paralysed by the economic disaster inherited from the Tories. He knew Ulster was a problem, but let it slide into 30 years of violence; he knew the unions needed to be dealt with, but flunked it. Heath's achievement was accession to the Treaty of Rome and, without the oil crisis and the miners' strike, he might have gone down in history as one of the greats. But he blundered into defeat and was ousted.
Thatcher learnt from the mistakes of the past but invented new ones. Some of her colleagues argue that privatisation was a happy accident. She had a strategy for dealing, once and for all, with the unions, but she impaled herself on an ideology for the economy, a prejudice on Europe and a poll tax for local government finance.
Blair's biggest challenger for intelligence has to be Attlee. But state education was Rab Butler's baby, the welfare state was Beveridge's. Attlee's contribution was the introduction of the NHS, the initial withdrawal from empire and a nationalisation programme too far. Hennessy, an avowed Attlee fan, argues that the postwar problems of deprivation were "so tough and so knotty that unless he hit the outer shell with five hammer blows simultaneously, it wouldn't have cracked it; that is why he kept sight on the essentials, and it was a remarkable success story on no money". Yet he relinquished office to the Tories for 13 years, his grasp of economics was poor and, as his biographer Kenneth Harris argues, he treated Europe as "a secondary matter".
If you want a measure of Blair's intelligence, strategic sense and political nous, consider how he has left William Hague flailing. He has egged on the Conservative leader to become more and more extreme on Europe, while peeling off senior figures such as Michael Heseltine, Kenneth Clarke and Chris Patten. Further, he has remembered how Labour was crucified on its tax-and-spend policies in 1992 and now, almost unnoticed, has set a similar trap for the Conservative leadership.
They have walked right into it. In 2001-02, with an election imminent, Blair and Brown plan a commitment to invest another dollop of £40 billion or more in health and education, transport, law and order in the three years after the election. But Hague has promised to cut the overall tax burden in his first parliament as prime minister. Just as Labour could not have increased spending without increasing taxes in 1992, Blair now argues - rightly - that the Tories could not cut taxes without cutting spending and therefore services. It is their spending "bombshell".
Peter Hennessy warns that prime ministers need to remember Enoch Powell's law: that political careers always end in failure. "We won't be able to test Blair's real mettle as a strategic thinker," he says, "until the problems come in battalions."
Time will tell. Blair could yet come a cropper. But the intelligence is formidable.
The writer is political editor of the "Express"