England expects ... a good TV show, and that's why 20 million of us will be glued to next Monday's 'Dianarama'. David Aaronovitch explains the Princess's big decision
Not since Edward II's friend Piers Gaveston was executed for sodomy in 1312 has there been a more unlikely confidant for royalty than the Panorama reporter Martin Bashir. An exposer of child abuse, a scourge of corrupt officials and the BBC's chief persecutor of the England football manager, Terry Venables, Bashir is a gossipy, intelligent elbow-tugger - an inveterate lover of intrigue. He is therefore the exact opposite of the usual Palace groupie, the ex-Guards aide-de-campes, the pompous peers or recycled newsreaders. What he has going for him, like other successful investigative journalists, is a reputation for straight-dealing with his sources and interviewees - he cannot afford to be a stitch-up merchant. And he was in the right place at the right time.

In the two weeks before Tuesday's announcement of the Princess of Wales's interview with Bashir all the staff at Panorama were aware that something was going on. The editor, Steve Hewlett, was hardly ever there. A mobile editing machine was sent (along with one of the Beeb's best tape editors) to an undisclosed address in central London. The fiction was given out that the intrepid Bashir was on the trail of a bent copper, and that the programme was therefore fraught with the kind of legal and PR problems that are the bane of BBC current affairs. In truth, it was to stop any chance of the Princess's interview being glimpsed by chatty journalists as they strolled along the corridor of the BBC's White City building. The ruse worked well.

Immediately "Dianarama" - as the forthcoming programme has been christened - became public knowledge, the speculation began about her motives for appearing and her wisdom (or lack of it) in doing so. Why was she doing this now? Why had she chosen Panorama? Was she not in danger of further discrediting the monarchy, just as it was hauling itself back into public esteem? Had it not been established through past experience that television is bad for royalty?

The Daily Telegraph, safely back in the hands of fogeydom after the demotic editorial interlude of Max Hastings, raised questions of its own about the BBC. What had happened to the traditional role of the BBC as a support and succour to the uniting institution of our nation, the monarchy? In agreeing to this interview without first obtaining the agreement of the Palace, opined the Telegraph, the BBC "took advantage of a lonely and unhappy woman" and was therefore "indistinguishable in its methods from the tabloid press". Or, to reconfigure the Telegraph's underlying question, is royalty not bad for television?

In most families the quarrels and recriminations happen in private. The settings for these desolate disputes are kitchens, hotel bedrooms and (judging by the Camden Town Sainsbury's) large supermarkets. Harsh words are spoken and, occasionally, crockery is thrown. Family members are caught up in the emotional arguments, and invited or blackmailed into taking sides. But royal families are full of people who have been reared in the public gaze. They marry in cathedrals, become Princes of Wales at strange ceremonies in Welsh castles, watch topless dancers in Tonga - and all in full sight of millions of television viewers. With hindsight it was inevitable that eventually they would also squabble and separate in full public view.

Nevertheless, when Diana's desperate feelings about her marriage were first partially revealed in Andrew Morton's Diana, Her True Story in 1992 it was the biggest breach in the dam of royal mythmaking for nearly a century and a half. For Charles it was - according to his biographer, Jonathan Dimbleby - "a humiliation of almost unendurable proportions". The nation was now talking about his real (as opposed to his "official") private life. The disastrous royal tour of India late the same year afforded viewers the spectacle of the "kiss that wasn't", as the Prince was rewarded for a spectacular score at polo by a lipful of empty air and a lot of headlines.

Then began the battle of the intermediates as "friends" and "sources" sought to put over the "real story" of each of the warring pair. Newspapers and books became the venue of choice for the marital conflict, "revelations" stood in for flung plates - and the whole nation became the orphans of a failed marriage - as each side blamed the other for dragging their 55 million children into the argument.

For both sides television has represented both the most potent - and the most dangerous - vehicle for getting their message across. The "humiliated" Charles was eventually persuaded by Jonathan Dimbleby that he would do himself good by revealing the real man to an inevitably huge audience on the occasion of the 25th anniversary of his investiture. The two-and- a-half hour documentary was, writes Andrew Morton, "the centrepiece of his long haul back to credibility". But, Morton says, Diana was aghast at the prospect. "From the moment the Prince informed Diana of the project she was on tenterhooks," Morton tells us. "She wondered aloud if it would burnish or tarnish Charles's image in the public's mind."

It burnished it. The usually mischievous Matthew Parris wrote the next day in the Times that he had been "very doubtful about whether the Prince should have committed interview with Jonathan Dimbleby", but that Charles had been a "commanding and intelligent presence, with bold statements to make". One of which was, of course, his admission of adultery.

When Martin Bashir first approached the Princess to see whether she might not be interested in discussing the constitutional implications of her marital status, he was almost certainly expecting the brush-off. But in the aftermath of the Dimbleby extravaganza Diana was seeking some televisual opportunity to show the real woman. To choose from among the hundreds of contenders, the best-known, heavyweight current affairs programme on television was a real stroke of genius. It suggests to the public that her appearance will be no addition to the semi-tabloid "kiss-and-tell" genre, but a serious and considered intervention in what she recognises to be an important and difficult question. Brilliant.

Ten years ago, however, the BBC might not even have been in the market. As the Telegraph suggests, the traditional relationship between the Corporation and the Palace has been a very correct one. There was until recently (and may be still) a woman at Broadcasting House charged with liaising with the Palace and through whom all requests to deal with any member of the Royal Family had to be routed. Every six months or so the corridors of Television Centre resound to a tannoyed announcement of "a major news broadcast" - in reality a dress rehearsal of how the BBC will react to a royal death. Just a couple of years ago the proposed schedule in such an eventuality was that BBC1 and BBC2 would cease functioning as two separate channels and - for two whole days - play nothing except news bulletins, various obituaries and "solemn music". This certainly showed real dedication to the role of maintaining the image and centrality of the monarchic institution. It also indicated a complete failure to to come to terms with how the nation had changed. The sudden surge in demand for satellite dishes and cable connections would have become one of the phenomena of the Nineties.

But these days the BBC can no longer afford to act as if it understood better than its viewers what is fit or fascinating for them to see. Some of this is down to the simple economics of competition in the broadcasting marketplace. But most of the change reflects the generational shift within the Corporation itself. Its executives, programme makers and journalists share the same fearless concern for the private lives of others that characterises the rest of society. They know that we are interested in what Diana has to say about her marriage, because they too are interested.

And that is the third side of this triangle. The couple reveal all in order to win the battle for approval. Broadcasters help them in response to the public mood. But why are we so bloody fascinated? In an age where deference has died and class is less important, where untold wealth is there for the price of a lottery ticket, why will 20 million intelligent Britons forsake Cracker and The X-files and tune in on Monday evening to an upper-class woman talking about her marriage?

Over 20 years ago I sat in the junior common room of an Oxford college renowned for its student radicalism. Together with the leather-clad members of the International Socialists and the kaftanned adherents of the International Marxist Group I watched Princess Anne plight her troth to Mark Phillips on telly. So we grew up with the royals on screen. In some sense they "belonged" to us - even if we held the institution in complete revolutionary contempt.

And the royals saga has often matched the spirit of the times. The bourgeois family at war was followed by a new Elizabethan age of post-war optimism, then a quiet solidity in the face of cold war uncertainties. But most recently it has reflected back to us our own crisis of the family - how our incurable romanticism has been disappointed by the reality of relationships. And so we have talked about their personal crisis as we talk about those of our friends and families - taking sides and perverse pleasure.

Diana stands for post-feminist women, who demand good sex, good talk and good fathers for their children - and she is mad as hell that the bloke she married couldn't deliver. Charles is not just a troubled prince, but a modern male, confused, upset, clumsy and uncomprehending - as emotionally retarded as the rest of us.

So we follow their progress through the small-screen, which betrays their hesitations, quivers and tics, wanting to know how it all turns out. Perhaps, in two years' time, the Prince and Princess will consent to joint therapy on screen, presided over by Dr Anthony Clare and watched by the entire country. It will be a logical step.

Screen love: a family on the box

1953: The Coronation, the first royal pageant to be broadcast live. Not only many people's first glimpse of the Queen, it is also their first glimpse of a television set: more than a million are sold before the big day.

1957: The Queen's Christmas message is broadcast for the first time on television.

1969: Richard Cawston's film Royal Family shows them as real people, joking, decorating the Christmas tree and barbecuing in the grounds of Balmoral. Watched by 22 million on BBC and 15 million when repeated on ITV. Now seen as the event that nudged open the Palace gates to public view.

1973: Princess Anne marries Capt Mark Phillips in Westminster Abbey. A massive television event shown around the world, it sets the tone (and the marketing strategy) for the subsequent weddings of Charles and Andrew.

1981: Marking their engagement, Charles and Diana give a blushing, giggling interview to the BBC's Keith Graves and ITN's Anthony Carthew. "Are you in love?" they ask. "Whatever love means ..."

1985: Charles and Diana, back before the cameras with ITN's Alastair Burnet, attempt to dispel rumours that their marriage is in trouble.

1992: The Queen's annus horribilis; also her 40th year on the throne, to mark which the BBC makes Elizabeth R, trailing her doggedly into state receptions and her box at Ascot.

January 1993: Sky TV screens its pounds 4m adaptation of Andrew Morton's book Diana: Her True Story, with Serena Scott-Thomas as the Princess of Wales. "Can't you ever leave my husband alone?" she snaps at Camilla Parker-Bowles.

November 1993: To Play the King, Andrew Davies and Michael Dobbs' sequel to House of Cards, includes a lonely, desperate monarch. A thinly veiled Charles? They couldn't possibly comment.

December 1993: Leaping the barricades, Prince Edward launches his own television production company, Ardent.

June 1994: Jonathan Dimbleby's two-hour film about Charles, in which the Prince admits his adultery. Only in November 1995 does his wife exact retribution, granting an interview to Panorama.