For the time being, the media regarded anything that was potentially embarrassing to the Royal Family as untouchable. The war had developed habits of self-censorship, which newspaper owners eager for Establishment respectability encouraged. A Fleet Street consensus believed that "disloyal" stories were dynamite: any short-term gain in circulation would be wiped out by a longer-term loss of reputation. The message from the public appeared clear. People wanted warm, comfortable and reassuring coverage of the Royal Family, and would not buy newspapers that offered anything else.

It was a climate that gave Buckingham Palace an extraordinary negative power, exercised in the person of the Queen's press secretary, Commander Richard Colville, an unbending ex-naval officer with no knowledge of the press, which he treated with a combination of distrust and lordly contempt. He felt little need to supply the press with information or facilities that did not directly support the impression Buckingham Palace wished to convey.

Even the BBC, ultra-sycophantic in all its coverage, was treated by the Palace in the run-up to the Coronation with disdain. Rules were tight, and transgressors sharply rebuked. In May 1952, BE Nicolls, Director of Home Broadcasting, wrote tentatively asking for permission to film the arrival of the Queen at Balmoral for Television News. The reply was a firm refusal. "Since Her Majesty and her family are going to Balmoral privately for a short holiday," wrote Commander Colville, "I do not think it at all appropriate." Journalists called him "the Abominable No Man".

But by the time of Commander Colville's retirement in 1968, attitudes were changing. His replacement, William Heseltine, believed that there was now a need to sell royalty to the public. Television was the key. The old Commander had regarded it as the work of the devil. His successor - with some encouragement from the Queen's consort - began to engineer a change of view. The result was Royal Family, a film for BBC television which provided a behind-the-scenes portrayal of what Commander Colville had dedicated his career to keeping hidden: the Queen's off-duty family life, including a scene of the Sovereign barbecuing.

"The film showed that the Royal Family was made up of ordinary people like the rest of us," says a close friend of the Royal Family, who had doubted the wisdom of the enterprise. "But when you discover they are ordinary people you have different expectations of them."

And once the Royal Family got into the business of revealing secrets, could it pick and choose? In later years, many looked back and said the film "started the rot". Yet though given exceptional licence, the film still presented the monarchy as it wished to be seen.

The Palace expected the press to feel grateful. This was naive. Appetites were whetted, that was all. Cynics detected another motive behind Buckingham Palace's sudden interest in raising the Monarchy's public profile: money. The Royal Family film happened in a year in which royal finances became an issue for the first time.

By the end of the Sixties, Elizabeth had already reigned longer than her father, prices had risen at an accelerating pace and wage and salary bills had grown disproportionately. But if the Queen's ability to meet official expenditure out of Civil List funds - fixed at the beginning of her reign - had been impaired, the expanding economy, and her immunity from tax, had greatly increased her private fortune. This was to become a matter of increasing public debate.

In 1971, a new Civil List settlement was made, but at a price. In the process, a House of Commons Select Committee went some way towards defining the monarch's official duties. It put the Crown more seriously on the defensive than at any time since 1936 and the Abdication. The Queen, through her close advisers, had to present a convincing case that she gave value for money.

At this point, the monarchy offered an icon of stability; the barbecuing Queen, leading the life of "a fairly conventional middle-class woman". It was an image of reassurance with its emphasis on family.

However, respect and envy for the domesticated embourgeoised Royal Family was not the same as a restoration of reverence. A lucrative trade in intimate royal photographs, established in the Sixties, was further stimulated in the Seventies by a circulation war among the tabloids. Yet even then the paparazzi did not challenge the "perfect family" ideal. On the whole, their images of royals relaxing heightened it.

It was the prospect of the marriage of the heir to the throne that marked the next stage. "Every working day of my five years at the Palace," says Ronald Allison, who was press secretary from 1973 to 1978, "there was a questioning of who Prince Charles would marry."

With the appearance in 1980 of Lady Diana Spencer, tabloid appetites, voracious at the best of times, passed all bounds. In a climate of total adulation, every aspect of the couple's lives was ruthlessly, caressingly examined. Critical faculties were suspended, praise overflowed.

How could the Palace-media nexus be questioned, when royalty succeeded in attracting such support? Articles appeared, congratulating royalty on, among other things, the brilliance of its public relations. But the danger was that excessive familiarity and availability would reap a whirlwind if and when the genetic lottery ceased to turn out good princes and princesses.

The fate of Margaret, the Diana of her day, should have provided a warning. To expose the Sovereign and her family to unlimited scrutiny, and to expect to find nothing but perfection, was to challenge fate.

After the wedding, Diana achieved a rapport with the media, based on a kind of secret notion that she was a fifth columnist and, unlike the family she had married into, remained human. However, nothing in her previous existence had equipped her to deal with being doorstepped almost every day of her life.

Then, in the late autumn, it was announced that the Princess was expecting a baby. The Queen and Court were finally stirred into defensive action. In November, the new press secretary, Michael Shea, took the unusual step of asking the editors of all the national papers to a special briefing at Buckingham Palace. Of those invited, only Kelvin MacKenzie of The Sun did not attend. At the briefing Shea made a plea for mercy. Afterwards, in a vain hope of reinforcing the moral pressure, the editors were introduced to the Queen, who circulated among them.

The psychology was faulty. Once, Shea's direct approach might have worked. Now, however, tabloid rivalry had become so intense that appeals to editorial good nature had no impact. Deference was dead. Two months later, The Sun and Daily Star published pictures, taken with powerful telephoto lenses, that showed Diana wearing a bikini and visibly pregnant. When Shea issued a statement that indicated the Queen's extreme displeasure, the two papers expressed regret - and alongside republished the offending pictures.

The December meeting had been a tactical error. Now that the basest of the tabloids had shown that requests from the Palace could be ignored with impunity, there was no holding their rivals back.

A critical moment in the altering image of British royalty came with a television show in 1987 called "It's a Royal Knockout." The project was an enthusiasm of the Queen's youngest son, Prince Edward, who had left the Royal Marines to work in the theatre. He was keen on a royal version of the slapstick programme, in which members of the royal family joined show business and sporting personalities who took part in ridiculous games.

"It was a terrible mistake," says one of the Monarch's friends. "She was against it. But one of her faults is that she can't say no." "There was not a single courtier," one recalls, "who did not think it was a mistake." Their advice was confounded by youthful enthusiasm and the Queen's maternal indulgence.

The programme was excruciating - "Give us a B. . ." bellowed the Duchess of York - and made the public stunningly aware that a sense of decorum was not an automatic quality in the Royal Family, and even that some members might be more deserving of their Civil List incomes than others.

In a way, it was the reductio ad absurdum of a process that had begun with "Royal Family." Perhaps it was even a logical outcome. After Knockout, the quality press joined in too. Over the next few years the Sunday Times played an important part in establishing the idea of a "royal problem" in the minds of a middle-class readership. The tone was not cheeky, as in the tabloids, but admonishing. Soon it was being pointed out that royal tax immunity was not an historic right but, on the contrary, had only been acquired in the 20th century. Taxing the Queen at 40 per cent would yield more than pounds 200m a year, "enough for a dozen hospitals", The Sun suggested gleefully. Before long even a staunch royalist such as Lord St John of Fawsley was conceding that the exemption had become hard to defend. In November 1992 - the annus horribilis - the Prime Minister announced that the Queen would begin to pay tax on her private income from the following year.

However, the cheekiness of the tabloid, and quality, press did not diminish. Calls for a slimmed-down monarchy became widespread, and the Queen, who had no critics who dared to reveal themselves early in her reign, now seemed to have few defenders among journalists and politicians. Though party leaders and other prominent members of the Establishment avoided joining in the chorus of detractors, few chose to give the existing system an open endorsement.

The republican movement had crept up on Australia in the Eighties in a way that served as a warning to the monarchy not to take the popular support at home, at any particular moment, for granted. At the time of the Coronation, monarchism had been almost as universal in Australia as in the United Kingdom; only 15 per cent of Australians, according to polls, favoured the idea of a republic. By 1991 an opinion poll in Scotland showed more Scots in favour of an elected president (48 per cent) than of retaining the Queen (43 per cent), should Scotland ever become independent.

Thus it was that the dreaded word, republicanism, previously the mark of a crank or a revolutionary, entered respectable and even Conservative discourse. Once the word had been uttered, it became inevitable that a debate that had been avoided for a hundred years would ensue.