During the recent celebrations to mark the Queen becoming our longest-reigning monarch, doubts were expressed about whether she herself had anything much to do with keeping “this anachronistic institution on the road”. Andrew Gimson, author of brief lives of our last 40 monarchs, wonders what would have happened under a Queen of different temperament.

The coronation in 1953 of Queen Margaret unleashed a tidal wave of adulation. As the only child of the late King, George VI, it fell to this beautiful young woman to symbolise her people’s hopes of a richer and more glamorous future.

In the words of the journalist Malcolm Muggeridge, her accession to the throne “was as though champagne were suddenly and unexpectedly to be served at a vicarage tea party”. Even during the coronation, the first great event of the television age, she carried herself with a sort of playful reverence as the Archbishop of Canterbury placed the Crown of St Edward upon her head.

Many of her subjects were already more than half in love with the new Queen. The roguish twinkle in her eye enraptured them. To them she could do no wrong. Her patronage of the Royal Ballet lifted Swan Lake to new heights of popularity.

With the benefit of hindsight, many will regard it as unfortunate that Queen Margaret imagined she too had attained a kind of invincible popularity. For soon after her coronation, she informed her Prime Minister, Sir Winston Churchill, that she had fallen deeply in love with, and had decided to marry, Group Captain Peter Townsend, a war hero 16 years older than herself who had entered royal service in 1944.

Churchill was aghast at the news. He told her the match was out of the question, for Townsend had recently got divorced. As recently as 1936, Queen Margaret’s uncle, Edward VIII, had been told by the then Prime Minister, Stanley Baldwin, that it was simply not on to marry a divorced woman, Mrs Simpson, and remain king. Unless the same logic were applied to the Queen, people would start saying Edward should never have been forced to abdicate.

At first, no one was keen for the Queen to abdicate, for if she did so before getting married and having children, her notoriously dim uncle, the Duke of Gloucester, would become King.

The very future of the monarchy was in danger. But Churchill was unable to bring home to Queen Margaret the risks she was now running. The Queen knew she was a devout member of the Church of England. Unusually for a woman in her position, she had often slipped off to listen to the Lent addresses at St Paul’s, Knightsbridge. She was certainly not a scarlet woman.

And this attempt to interfere in her personal life and prevent her marriage struck her as a bid by the stuffy, pharisaical Establishment, most of whose members were about 60 years older than herself, to turn her into a mere puppet and make her existence a complete misery.

So she told Churchill she proposed to take Henry VIII as her model. Her governess had taught her how Henry, when prevented by the Church from marrying Anne Boleyn, had resolved, in Macaulay’s words, to remain an orthodox Catholic but “to be his own Pope”.

Queen Margaret informed the Prime Minister that she proposed to remain an orthodox Anglican but “to be her own Archbishop of Canterbury”. Like Henry before her, she would marry the person who was essential to her happiness, and would carry the Church and the wider public with her.

This startling news precipitated the stroke which disabled Churchill at the very moment he was needed to head off disaster. No other politician had the authority needed to get on top of the situation.

While Churchill retired to Chartwell to convalesce, London was swept by rumours that the Queen and Townsend had been sighted at Chelsea Registry Office, after which they had attended a service of blessing at St Paul’s Knightsbridge. The foreign press reported these preposterous rumours in lurid detail. The British press repeated the foreign stories, and denounced them as obviously untrue.

Townsend now attempted to do the decent thing. He announced that he would under no circumstances marry the Queen, after which he fled the country.

But his act of renunciation seemed to confirm that the story of the projected marriage was in fact true. The fairytale of the coronation gave way to endless, highly inaccurate coverage of a squalid affair with a married man.

The Queen was profoundly hurt by the treatment she received from the British press. As she observed when she appeared on Desert Island Discs, “I’ve been misreported and misrepresented.”

The public in turn felt let down by the Queen. From being unwilling to believe anything bad about her, it became unwilling to believe anything good.

She was said, in the succeeding years, to have had affairs with a number of unsuitable men, including a photographer and a landscape gardener.

People began to wonder what the point was of having a monarchy which reflected such discredit on the country. A growing tide of republicanism made itself felt. If the United States, France and Germany could get on quite well without a monarch, that must be the modern way to go.

So when Queen Margaret announced, to general stupefaction, that for the sake of her health she intended, during the winter months, to carry out her functions from the Caribbean island of Mustique, where her heating bills would be very much less and the Prime Minister would be welcome to visit her any time he felt in need of her advice, she found she no longer had any reserves of loyalty to fall back on.

A monarchy which had existed for over a thousand years was swept away by an row about a divorce, followed by a row about a holiday island. The British Republic was born, with Selwyn Lloyd, a man of uninspiring demeanour but unimpeachable integrity, as its first President.

The former Queen, who settled permanently in Mustique, observed that divorce had become pretty normal among her former subjects, as had foreign holidays in sunny parts of the world. Her only fault, she said, was to be somewhat ahead of her time.

Gimson’s Kings and Queens is published by Vintage Digital.