Theatre: The Charles and Di show. Or is it?

The Royal Family indulging in a bit of extra-marital is hardly new. But can they get away with it at the Royal National Theatre?

Consider this scenario. We're talking here about the Prince and Princess of Wales. He only marries her because she's a virgin with the right genetic connections and because he needs to beget an heir. Immediately, though, there are three - possibly four - people in the marriage. The couple quickly produce a child who can succeed, but succeed is precisely what their relationship does not.

The two of them start to use the press in a publicity campaign against each other. She becomes persona non grata with the Royal family, goes abroad and takes up with a dubious partner of foreign extraction. The people of England, on the whole, side with her in this emotional contest. If never crowned Queen, she at least has the satisfaction of being the Queen of People's Hearts. Indeed, they line the streets for her. Oh, and she meets a premature, tragic end. The suspense is not exactly killing, is it? We all know to whom this sorry saga refers. So, come on down Prince George of Hanover and Princess Caroline of Brunswick.

On 9 December at the Lyttelton Theatre there is the premiere of Battle Royal, a new play by Nick Stafford which focuses on the discord - marital and national - surrounding this mismatched Regency couple. I don't think it's rash to predict that we will hear the patter of not-so-tiny parallels.

What gives the event added piquancy is the venue. In the theatre that gave us The Madness of George III, we now have the edifyingly unedifying exploits of his sprog, George IV, to be impersonated by Simon Russell Beale - an actor with a consummate talent for playing difficult sons who compensate for parental rejection by indulging themselves.

There's a further twist, for the Lyttelton is part of the National Theatre or, rather, the Royal National Theatre as it was dubbed in 1988. Does association with royalty perform any particular magic in such a context? Bob thinks not: "What good did it ever do a leper to have his hand shook by royalty? He's still a leper. They don't leave any money behind on his bedside table, do they?"

Surprisingly, the aforementioned fictional Bob is not from some radical Seventies play at the Royal Court (where "royal" in the name is just an ironic relic, not the mark of favour). No, Bob is a character from a healthily sceptical Australian play for children, Two Weeks With the Queen (about a 12-year-old boy who embarks on a touchingly naive scheme to waylay Her Majesty and secure her help for his dying younger brother), which received its British premiere at - where else? - the Royal National Theatre.

That's the kind of bracing contradiction you can get away with in a constitutional monarchy. Just as atheism is (as it were) a broad church and one of its worshippers might well deliver a sermon in St Paul's, so the debate about the meaning and function of royalty can scarcely exclude itself from the key public arena that is the Royal National Theatre. And there has been some delicious backstage farce in the angling for royal favour.

When Lord Rayne, the Chairman of the Board, first put out feelers in this direction, it was his bad luck to meet at the Home Office the very same senior civil servant who had had to consider whether or not to prosecute The Romans in Britain. This was the notorious Howard Brenton play that was taken to court by Mrs Mary Whitehouse for "procuring an act of gross indecency". So, given that the spectre of several buggered ancient Celts arose between them, it is not surprising that Lord R received a dusty answer.

And when royal favour seemed to have been safely bagged and the Queen duly booked to appear at a 25th anniversary gala, there was a boardroom brouhaha about Alan Bennett's A Question of Attribution. Was it not, the suits gasped anxiously, an act of lese-majeste to impersonate a reigning monarch on stage (even if the imitator was Prunella Scales)? For about a fortnight, it looked as though the National's then artistic director, Richard Eyre, might have to threaten to resign to get the piece on. The irony, of course, is that there has surely never been a more attractive dramatic portrait of a monarch.

The great scene in that work comes in the comic confrontation between the Queen and her surveyor of pictures, the not-yet-unmasked spy, Sir Anthony Blunt, who has been granted immunity in order to name names. How much does the Queen know about this behind-the-scenes horse-trading? The question is left tantalisingly ajar in a series of brilliant exchanges where Her Majesty's brisk, philistine, false-footing manner seems like an stalking horse for the acuity and wit which, presumably out of sheer modesty, she keeps so well disguised as dullness in her real-life public engagements.

If Battle Royal does, indeed, point up contemporary parallels, it won't be the first time this has happened in the Lyttelton, though Alan Bennett writes that, in the case of The Madness of George III, these were fortuitous or the inevitable result of history's tendency to repeat itself. In A Question of Attribution, performed before Tony, Cherie and their burgeoning family dropped anchor in Downing Street, the line that always got the biggest laugh was HMQ's "Governments come and go. Or don't go.")

And if there is any republican resonance, this, too, will fall into an honourable tradition. In 1996, Tony Harrison, the poet who last year publicly dissociated himself from the race for the laureateship, did a National Theatre adaptation of Victor Hugo's anti-monarchical 1832 play Le Roi S'Amuse (later turned into the opera Rigoletto by Verdi). Harrison gave his version edge by switching the action from the court of Francis I to that of the future Edward VII, whose unfeeling lust destroys a jester-equivalent in the shape of music-hall comedian.

Lest monarchists take alarm, though, it should be noted that theatre has almost an in-built bias in favour of princes, kings and queens. It's interesting that in the two most high-profile republican plays of recent years, Sue Townsend's The Queen and I and Divine Right, the royals have had to be co-opted to the enemy cause to make the republicanism theatrically sympathetic. Given the massive gulf of privilege, it may seem paradoxical that audiences tend to identify with crown-wearing characters; but this is because, at some level, they come across as heightened metaphors of the existential human predicament. It's a phenomenon that was hilariously illustrated last year by Love Upon the Throne, the Charles and Diana story as told by the National Theatre of Brent (not yet Royal, though it's surely only a matter of time). All the parts in their extravaganza ("This year has truly been my anus," declared the Queen) were performed, with delirious ineptitude, by Desmond Oliver Dingle (who is luvvy self-importance in a blazer) and his gormless, insecurely toupeed sidekick Raymond.

Two incompetents thrust by fate into roles that prove too big and hard for them, it's the story of all our lives, on this great stage of fools. So here's a tip for all would-be writers of republican drama. If you want to rid the country of royals, you've first got to make them leave the stage.

`Battle Royal' begins previews at the Royal National Theatre, London from tomorrow (0171-452 3000)