Back in 1980 some National theatregoers got so upset when Caesar’s soldiers raped a harmless Druid in Howard Brenton’s Romans in Britain that they overlooked the rather more disconcerting point the playwright went on to make, which was that we English were similarly sodomising Ulster. But the theatrical agent provocateur has softened. Here he is at the same address, presenting a dramatic biography of Harold Macmillan which, even though it ends before the One Nation Tory belatedly won over the Left by denouncing Margaret Thatcher for “selling off the family silver”, is surprisingly sympathetic to - well, the man who is almost its hero.

Almost, because Macmillan does some shifty-seeming things during Howard Davies’s production, such as withdrawing his support for a Suez invasion he had fiercely supported. But there was good reason for that, since he was Chancellor and an outraged Eisenhower was about to wage economic war on Britain. And as played by Jeremy Irons, the grandee-to-be is no opportunist but a shrewd, canny, withdrawn figure who conceals a melancholy and even a despair beneath an urbane exterior, is more the thwarted idealist than the cynic he sometimes seems, can be quietly steely and unaggressively tough, and invariably radiates calm when he’s under fire, which he literally is in the first of Brenton’s four engrossing acts.

This involves Macmillan’s First World War, in which Pip Carter, playing the gangling, eager, ultra-patriotic young Harold, gets the worst of his five wounds during a Battle of the Somme that’s evoked almost as ferociously as the air crash that nearly kills him in a second act stretching from 1938 to 1943.

Each time he is genuinely heroic, and almost more so when he risks political death by joining Churchill in his rejection of appeasement. This, too, is enterprisingly staged, with Terrence Hardiman’s Chamberlain delightedly waving his agreement with Hitler, turning and, a moment later, glumly announcing the outbreak of war from Downing Street.

And so to Suez, Macmillan’s premiership, his downfall after the Profumo disaster, and, all along, his seemingly serene but inwardly pained tolerance of the long affair between his wife, Anna Chancellor’s Dorothy, and Robert Glenister’s fleshy Bob Boothby. Political success comes at personal cost, or so Brenton suggests, adding the inference that Eton may have left Macmillan either homosexual or sexually dead or a bit of both.

True, there are clunky moments, with characters saying things like (Dorothy on sex) “it makes me feel alive” or (Harold on Suez) “this is an hour of maximum danger”. True, Brenton doesn’t always solve the problem of conveying necessary facts through believably natural dialogue. True, too, the device of having Carter’s Young Mac hang around the stage in his Army uniform, representing the ambition his pushy mother forced Macmillan to keep feeling, has outlived its usefulness by the evening’s end.

Nevertheless, the play is two or three cuts above the usual theatrical bio. There are consistently good supporting performances, from Anthony Calf’s vain, edgy Eden to Ian McNeice’s Churchill, who looks a bit like a bloated dwarf but does catch some of the giant character. And all along Irons manages genuinely difficult feats. To be self-effacing yet in command. To aim for power without quite wanting it. To yearn for a better world, perhaps even one where the privates he saw sacrificing themselves in the trenches were able to take democratic control of their own lives, yet to be at ease in the mess of party politics. To attain success yet see through it and, at times, wish for death. To watch what he suspects is his own moral decline. To be inscrutable. In short, to be Harold Macmillan.

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