Jeremy Irons shines in Never So Good

Who would have thought it? Howard Brenton, the former dramatic firebrand of the hard Left, and the man who notoriously brought simulated anal rape to the stage of the National Theatre in The Romans in Britain, has written a play that is deeply sympathetic to a Tory prime minister.

The dramatist, who becomes ever more interesting as he grows older, with fine recent plays about St Paul and Abelard and Heloise to his name, originally set out to write a satire about Harold Macmillan.

But the more Brenton researched the man once dubbed the great actor-manager of British politics, the more he came to admire him, and this gripping, compassionate and often delightfully comic play strikes me as his finest achievement to date.

There are echoes of earlier works - Coward's Cavalcade, and Alan Bennett's Forty Years On spring to mind - in a play that follows Macmillan from his schooldays at Eton to his final years as the stooped and ancient statesman who accused Margaret Thatcher of selling off the family silver.

In telling the story of Macmillan this is a play that also tells the story of Britain in the 20th century, from the courage and carnage of the battlefields of the Somme to the decadence of the Profumo affair and the satire of Beyond the Fringe.

Brenton suggests that between them Christine Keeler and Peter Cook did much to end the ingrained British habit of deference and left Macmillan himself looking like a man entirely out of tune with modern times.

In the dramatist's view, it was the First World War that shaped Macmillan. Injured on five different occasions, the horrors of the trenches left him with a chronic sense of survivor's guilt and an abiding sympathy for the working class who served their country so bravely.

His one-nation Toryism was viewed as downright socialism by his pushy American mother who felt her son lacked the last ounce of steel that would propel him to the top. In this she was mistaken.

In a highly effective conceit, two actors play Macmillan. Jeremy Irons gives one of the finest performances of his career as the mature husband and politician, combining charisma with vulnerability, high principle with low cunning, and political success with personal hurt.

The pain caused by his wife Dorothy's long affair with Bob Boothby is caught with especially fine and affecting delicacy, but Irons also captures Macmillan's humour, intelligence and resilience, and by the end you feel you have seen a complex man in the round.

But the mature Macmillan is constantly shadowed by his own younger self, the youthful officer who ought to have died in the trenches, and who constantly questions the older man's motives and actions. In a difficult role, which often involves little more than watching the older man in action, Pip Carter helps suggest the inner tensions of Macmillan's character.

Director Howard Davies seizes all his chances, achieving many virtuosic moments in a production that mixes the intimate and the epic. A sedate dance at The Ritz gradually morphs into the battlefields of the First World War, while the story of the Suez crisis plays out like a gripping thriller.

Among the supporting performances, Anna Chancellor's guilt-stricken Dorothy, Robert Glenister's coarse Bob Boothby and Ian McNeice's wicked impersonation of Churchill shine particularly brightly in a drama of rare ambition, intelligence and human sympathy.