The Queen personally intervened to ensure that Prince Philip rather than Princess Margaret would have acted as regent if she had died in the early years of her reign.

In July 1953, just a month after her Coronation, the Queen lobbied for a change in the law to prevent her sister ever becoming regent, Government papers show.

Under the terms of the Regency Act 1937, had the Queen died or become incapacitated, Prince Charles would have succeeded her. But as he was just four years old in 1953, Princess Margaret would have taken over as regent until he was 18.

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Queen Elizabeth, left, lobbied to change the law in 1953, so Prince Philip, rear, would take over as regent instead of her sister Princess Margaret, centre, in the event of her death until Prince Charles was older

Files obtained by this newspaper under Freedom of Information laws show that the Queen’s suggested change caused considerable discussion in the then Government, and that the Queen wished to see the change to the law brought in as soon as possible.

Some Ministers were worried the public might regard any changes as an affront to the Queen’s younger sister.

They were also worried about the timing of any new legislation, given continued speculation about Princess Margaret’s private life. At the time she was involved in a romance with RAF Group Captain Peter Townsend, who was considered an unsuitable husband for her because he was divorced and a commoner.

One document that details a Cabinet discussion of July 6, 1953, expressed the fear that ‘if the Bill were introduced at this juncture, it might give rise to controversy owing to the publicity given by certain newspapers to reports linking the name of Princess Margaret with that of a commoner recently divorced’.

There were fears surrounding Princess Margaret's relationship with Group Captain Peter Townsend, pictured, who was a divorced commoner

The Government’s preferred option was to delay the new legislation until the autumn, during the Queen’s planned tour of the Commonwealth. Ministers hoped that speculation about Princess Margaret’s private life would have died down by then.

But the documents show that the Queen did not want to wait. At a Cabinet discussion on July 8, it was reported that ‘the Home Secretary [Sir David Maxwell Fyfe] said the Queen’s Private Secretary had also spoken emphatically to him in favour of immediate legislation’.

Significantly, the files stress that the Queen’s position had the full support of Princess Margaret.

A briefing note for a Commonwealth Heads of Government summit held in London on June 5, 1953, stated: ‘The Queen’s wish in this matter was shared by other members of the Royal Family, and in particular, by Princess Margaret.’

Prime Minister Winston Churchill backed the Palace’s view that the change in the law should not be delayed, although his ability to influence matters was limited because a month earlier he had suffered a stroke.

In a memo dated July 8, 1953, Churchill was dismissive of the concern over press coverage, writing: ‘The world does not come to an end because there is a caterwaul for two or three days... I am for going ahead and am only sorry I cannot take an active part in the dispute.’

In the event the Regency Act was passed in November 1953.

Speculation about Prince Margaret’s relationship with Townsend continued but in 1955 it was announced the couple would not marry. The Princess later married Antony Armstrong-Jones, the Earl of Snowdon, whom she divorced in 1978. She died in 2002 aged 71.

Royal biographer Hugo Vickers said the Queen wanted the Bill to go through to ensure that the Duke of Edinburgh had a greater degree of responsibility.

He added: ‘I think the change was entirely logical. It was perhaps motivated by five per cent negativity towards Princess Margaret and 95 per cent positivity towards the Duke of Edinburgh.’

A spokesman for Buckingham Palace declined to comment.