Instead it fell to her eldest son Prince Charles, 73, to deputise, in the most important state engagement yet in his record-breaking time as her heir.

When his mother dies, he will be king and opening parliament for a new session will be one of his most important constitutional duties as head of state.

Other than the last-minute change of personnel, there was little to distinguish the centuries-old ceremony from previous ones in the putative “mother of all parliaments”.

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Two mounted divisions of the Household Cavalry regiment formed a “secure passage” for the limousine carrying Charles and his wife Camilla from Buckingham Palace.

Regalia symbolising royal authority was paraded – the bejewelled Imperial State Crown, the Great Sword of State and Cap of Maintenance.

The red-coated Queen’s Body Guard of the Yeoman of the Guard – the “Beefeaters” – kept watch. Liveried parliamentary and government officials processed.

A ceremonial search of the cellars of parliament was conducted – a throwback to when a gunpowder plot was foiled before the opening of 1605.

The door of the House of Commons was slammed shut in the path of Black Rod, an official from the unelected upper House of Lords, to symbolise the independence of the elected lower chamber from the monarchy.

One member of parliament was held “hostage” at Buckingham Palace to ensure the safe return of the monarch, another throwback to more troubled times.

Then MPs filed into the Lords, their daywear in contrast to the peers in red and white ermine robes, to listen to the speech.

Charles, dressed in the ceremonial uniform of admiral of the fleet, complete with a sheathed sword, arrived to a trumpet fanfare.

The Prince of Wales has had a lifetime to prepare for such occasions. He showed no sign of nerves, smiling and occasionally stopping to chat as he made his way to the chamber and the platform bearing the consort’s throne.

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Camilla – a future queen consort – sat to the left of the future king. His eldest son, Prince William, 39, to his right, getting his first taste of an occasion he will also have to perform one day.

The golden throne of the monarch, who was said to be watching on television from home, was removed. In its place was the crown on a velvet cushion.

At 11:34am, Charles began reading. Such was the eleventh-hour change of plan, the government still circulated the original version of the speech.

“My Government’s priority is to grow and strengthen the economy and help ease the cost of living for families,” it read.

“My Government will level up opportunity in all parts of the country and support more people into work.

“My Ministers will continue to support the police to make the streets safer, and fund the National Health Service to reduce the Covid backlogs.

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“In these challenging times, my Government will play a leading role in defending democracy and freedom across the world, including continuing to support the people of Ukraine,” the distributed speech said.

Charles – not yet king – changed it to “Her Majesty’s Government” and “Her Majesty’s Ministers”.

At 11:43am it was all over. A military band played “God Save the Queen”, as he left. “Long live our noble Queen!” the national anthem exhorted.

After Tuesday, many were understandably left wondering, for how much longer?