Monarch preparing to mark milestone

On Wednesday, she will pass the record set by her great-great-grandmother Queen Victoria who, Buckingham Palace has calculated, reigned for 23,226 days, 16 hours and 23 minutes.

There has been speculation a celebratory private event is planned but it is understood that in keeping with the Queen’s business-as-usual approach it will be a normal working day for the monarch with no special dinner party.

At this time of year the Queen is taking her traditional summer break at her private Scottish home of Balmoral. Yesterday she was pictured arriving with the Duke of Edinburgh at Crathie Kirk for a Sunday church service near Balmoral.

On the day she passes Victoria’s milestone, the monarch, joined by the Duke of Edinburgh, will open the new Scottish Borders Railway and take a steam train ride on the new £294 million railway.

Members of the Royal Family including the Prince of Wales will also be working. Charles will be filming a documentary with TV presenters Ant and Dec, believed to be about his Prince’s Trust organisation.

A royal source said: “You need to remember for the Queen this is a date whose calculation rests on the death of her father and great-great-grandmother, that naturally colours the way she sees it.

“While she acknowledges it as an historic moment, it’s also for her not a moment she would personally celebrate, which is why she has been keen to convey business as usual, and no fuss.”

Historian Dr Kate Williams said: “It’s a very significant milestone. The Queen will become the longest reigning British monarch in history.”

The milestone comes as a survey revealed knowledge of the Commonwealth among British schoolchildren is a cause for concern, after it found just half of children polled knew the Queen was its head.

Only 7 per cent of those surveyed could identify the association’s flag, while less than a quarter asked to choose three member countries from a list could do so, a poll for the Commonwealth Exchange found.

Princess Elizabeth became Queen Elizabeth II when she was 25 on the death of her father King George VI on February 6 1952. The Queen passes record at around 5.30pm on Wednesday when she will have reigned for 23,226 days 16 hours and approximately 30 minutes - but the exact moment she became Queen is hard to calculate as George VI died in his sleep in the early hours of the morning.