It's hard not to treat this statement with as much suspicion as one would a piece of unattended baggage during a terrorist bombing campaign. Desmond Dingle's all-embracing enthusiasms are the stuff of satire. Each production undertaken by the National Theatre of Brent, since its rapturously received inception at the 1980 Edinburgh Fringe, has attempted to tackle a lofty theme with due reverence and attention: the charge of the Light Brigade, the black hole of Calcutta, the French Revolution and the life of Christ are just a few. But because of the size of the company - just Dingle and a put-upon sidekick - each show, solemnly performed in matching grey suits a la Gilbert and George, always falls far short of its grand intention.
The disparity - which grew out of a period in the late Seventies when Barlow was appearing at a children's theatre in Brent Park and at the National - has the potential to be devastatingly funny. When applied to the most famously mismatched couple of the century, it also has the potential to be intensely controversial. That a man (John Ramm, who plays Dingle's assistant, Raymond Box) will be taking on the role of Diana might be viewed as more than simply incongruous to some. To those who've paid to show respect at Althorp, it could be sacrilege.
A few other shows in Edinburgh this year have raised eyebrows: Pip Utton's Adolf, an address by the Fuhrer to an imagined audience in Berlin at the hour of his suicide; and Myra and Me, a play about a group of Hull graduates, one of whom has been commissioned to make a TV programme about Hindley. But these represent old taboos, prompting tired knee-jerks of disapproval. And neither are billed as comedies. If there has been no outcry about Love Upon the Throne as yet, that may be because the National Theatre of Brent is not returning calls from tabloid journalists. And there have been calls.
Barlow suggests that the absurdly pompous Dingle has no idea why his shoestring productions are so popular because he is unable to see their funny side. However, he cannot plead the same obliviousness if splutters of laughter are generated at Diana's expense. He explains himself, with watchful, wary eyes, during a rehearsal break, keeping a very straight face throughout.
In the same way that he has finally reached his character's age (51), so he differs very little from Dingle when it comes to assessing the potential for controversy. The production, which was due to start rehearsals on 1 September last year, was immediately shelved at the news of Diana's death. This was not done, he stresses, because of fears about the show's content, but because "everyone was very raw about her, in a state of shock. I was deeply moved, too. Only horrible, hardened old cynics aren't prepared to admit that the whole country was knocked back by it."
Six months later, however, he returned to the story, prepared to lop off a scene here or there. This isn't the story of Diana, he insists, but "the story of Charles and Diana. It's a play about a relationship, a relationship that was fraught with many difficulties and which finally ended. It begins at their meeting and ends at the point of divorce. Diana's death is not alluded to at all."
But even so, doesn't the fact of her death change everything? He shakes his head. "The relationship between Charles and Diana is one of the great mythic relationships of our time. It still needs addressing. Their marriage went horribly sour, as many people's do. To an extent, they were already up there on stage, acting it all out for the rest of us."
To deny the reality of her life is to be in denial about her death, he believes. "Everyone knows that Diana had a huge personal struggle. There's a danger of treating her as a saint. If she were alive now, she would be treated as she used to be by the general press, as this outrageous, fascinating but indulgent creature. I also think that if she were alive now she would laugh at the lightness of this show."
That light playing style didn't immediately suggest itself when Barlow first considered writing something three years ago. "I initially thought it might work as high opera. It certainly couldn't be staged naturalistically, or it would descend into a soap opera. Then I realised that I already had a way of telling the story that would retain the truth of the situation while achieving some kind of distance. Comedy is an enormous distancer. It allows you simply to observe what is happening." The effect, he hopes, is quasi-Brechtian, noting that Ramm's "Diana" is "not remotely a female impersonation. He doesn't attempt to be her and in a weird way he gets a quality in her that a woman couldn't get, because she would be too close to it."
And in a weird way, he may be right. I am briefly allowed in to watch director Martin Duncan (a Brent regular) putting the pair through their paces. What I see is both haunting and ridiculous in its suburban ordinariness. They walk through the scene in which Diana accidentally picks up the phone to hear Charles talking dirty with Camilla - the dilemma turns into a spot of audience participation: "Do I bury it under the carpet or do I listen in?" he asks, in a feeble Essex whine, before Dingle steps out of character and tells him to shut it.
The scene no one in the room can resist chuckling at - in which Diana runs amok in the Palace having told Charles she's going to throw herself downstairs rather than watch the Queen's Christmas Message - is later axed. But there is no getting away from the fact that there are plenty more gags where that came from. The moment divorce is decided upon is played as a slip of the tongue. "No," says Barlow's Dingle's Charles gleefully: "Divorce is what you said, and divorce is what you'll get!"
"If people get outraged by the idea of this, there's nothing I can do," Barlow says. "But if people come and see it, I would be very surprised if they are. I believe our heart is in the right place." Still, it might be worth leaving through the Assembly Rooms backdoor tonight, just in case.
'Love Upon the Throne', Assembly Rm, Venue 3 (0131-226 2428) 4.30pm, Tomorrow to 5 Sept; then Bush, London, W12 (0181-743 3388) 8-26 SeptReuse content