Harold Brenton's new play about Harold Macmillan reveals some surprising right-wing sympathies

There are many playwrights you might expect to write a sympathetic play about the Conservative Prime Minister Harold Macmillan, but Howard Brenton is probably not one of them. This the man who, along with David Hare, David Edgar and Caryl Churchill was at the epicentre of Britain's blazing maelstrom of left-wing theatre that dominated the 1980s. He's the man who got the establishment in a tizz with the infamous Romans In Britain (1980), whose scenes of simulated buggery prompted Mary Whitehouse to mount a private prosecution against Michael Bogdanov, the play's director. He's a socialist and an atheist, a mischievous and sometimes pugilistic iconoclast who has carved a prolific career out of attacking right-wing institutions and sending up England's romanticised notions of its own mythology. So what's he doing writing what he calls "an apology to the memory" of a Tory, and one who stood so emphatically for the old England of empire at that?

Brenton chuckles at all this – despite his fierce and formidable appetite for provocation, he tends to chuckle rather a lot. "Well, I wanted to write about a democratic politician whose life encompasses a fair part of the century," he says. "And I also thought that I really ought to write something about the Tories. I really intended the play to be a satire, but actually, the more I researched it, the more I began to take Macmillan very seriously. He was a magnificent politician, but his downfall, clouded by scandal, was very cruel."

Never So Good (the title paraphrases Macmillan's famous – albeit oft misquoted phrase: "most of the people in this country have never had it so good") is the second Brenton play to be commissioned by the National Theatre under its artistic director Nick Hytner and heads a spring season on the South Bank that's dominated by new writing. A drama in four acts, it traces the life of Macmillan (played by Jeremy Irons) from First World War, where he was terribly injured, right through to his last days in office as Conservative Prime Minister in 1963, having taken over from Anthony Eden following the Suez crisis.

In fact, Brenton describes it as a play about three crises: "There was Munich, when Macmillan was one of Churchill's lieutenants in opposition against Neville Chamberlain, then there was Suez, when Macmillan was Chancellor of the Exchequer, with all the infighting behind the scenes, and finally there was the Profumo affair of 1963 which helped topple him," he says. "Really I was trying to put on the stage how democratic politics work behind closed doors. How the ruling elite deals with the problems of the time. And the more I read about it, in particular the unpublished diaries in the Bodleian Library in Oxford, the more I realised just how fragile the state is."

Brenton has always been fascinated by the mechanics of power and the men who exercise it. Pravda, perhaps his greatest play and co-written with David Hare at the height of Thatcherism, was a satire of the newspaper industry and featured a right-wing media tycoon intent on taking over Fleet Street. The Churchill Play (1974) offered a dystopian vision of a Britain run by a fascistic and draconian government; intriguingly one that sanctioned detention without trial and the use of torture. In the case of Never So Good, however, it sounds as though Brenton set out to write a play about politics and government, and ended up writing about a man instead. "Oh yes, I think Macmillan is a very tragicomic figure, perhaps more tragic than comic," he says. "When I was growing up he seemed to epitomise everything we hated in the 1960s, that old fuddy-duddyness, and out of touch Edwardian England, banging on about the First World War and playing Elgar all the time. But when he finally came to power he just couldn't get to grips with it."

In fact Macmillan ended up becoming thoroughly disillusioned with power. "His perspective on things tended to the fatalistic. He also had a sense that chaos was always near. His famous statement, 'Events, dear boy, events,' conceals an almost metaphysical thinking about what public life constitutes.

"He was trying to re-establish Britain as a major power in the world; trying to reconcile leading in Europe with being a close ally of America... we are still troubled by that problem."

When Macmillan came to power, almost overnight England had become a modern country infatuated with the idea of personal freedom, transformed into something that this hangover from empire no longer understood. Brenton has some sympathy with this he has his own experience as a playwright who moved from being at the centre of the zeitgeist to becoming almost a total stranger to it. He might be enjoying a flourish of creative activity on the stage now, but his real heyday was the 1970s and 1980s, when, as he puts it, he and David Hare were building up a "head of steam" writing a string of radical plays that gleefully broke with the theatrical and political orthodoxy of the times. By the mid-1990s he had virtually disappeared, writing nothing of significance for the theatre for almost a decade (although he did prosper in TV instead, writing for the spy drama Spooks).

Talking of those times, does he buy the prevailing idea that the fall of the Berlin wall ushered in a new political lethargy that resulted in the emerging generation of playwrights dropping big ideas for more inward looking social dramas? "It's true that the 1980s contained several plays that had big satirical targets," he agrees. "Protest dramas of defeat were very popular back then. But when the wall went down we realised we'd been writing a lot of cold war plays about the paradox of the East-West split, and suddenly the shape of the world had changed. And people thought: 'look at all these old cold war playwrights of the left. Their agony is so out of date.' And if your agony goes out of date, you really are in trouble."

In recent years, Brenton has made a triumphant return. Paul, a secular reworking of the story of St Paul, was a big hit at the National, although at one point the play was in danger of being overshadowed by the controversy that preceded it: the theatre received over 200 letters of complaint. Brenton dismisses it all as rather silly. "They thought it was going to be some terrible outrage: Nick Hytner, producer of Jerry Springer plus Howard Brenton multiplied by St Paul. But when they saw it they realised that it was actually a serious play and went away."

Then there was In Extremis at Shakespeare's Globe, another forensic inquiry into the nature of faith, this time through the story and rationalist teachings of the medieval lovers and scholars Abelard and Heloise. Both plays chimed with a new cultural climate in which suddenly faith rather than politics had become the new ideology. But Brenton dismisses that with both plays he was responding to something in the air. "The timing was just good luck," he says. "With Paul, it was a case that I'd always wanted to write a play about religion... and Paul was the obvious man to try and write about. And lo and behold, it just so happened that at the same time, people had become very interested in issues of faith."

So in writing about Macmillan, has this former fire-breathing radical mellowed with age? "When you are 65 you start to thinking first and last things," he says soberly. "In writing about this politician who wasn't much older than I was when he went down: it sounds vacuous but you really begin to think of things such as birth and death more. Your satirical days are over. Instead you try to write dramas that are more about the human predicament."

To 24 May, Lyttelton Theatre, London SE1 (020-7452 3000)