The Queen will soon make history when she becomes the longest reigning British monarch – but on the day it will be business as usual for the head of state and her family.

Today, she passes 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 that 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.

But 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 and Duchess of Cornwall 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 which celebrates its 40th anniversary next year, while Camilla will visit the ITV studios in London to celebrate the organisation’s 60th anniversary.

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 a 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 Kate Williams described the length of the Queen’s reign as a great source of strength for the monarch.

“It’s a very significant milestone. The Queen will become the longest reigning British monarch in history. She came to the throne when she was older than Victoria. Victoria was only 18,” Williams said.

“It shows that our female monarchs last the longest. The Queen’s longevity is a great source of her strength and popularity. She has lived through World War II and throughout the 20th century. Many people will not have known a different monarch.”

Queen Victoria, who died in 1901, acceded to the throne on June 20 1837 and became the figurehead of a vast empire amid great industrial, cultural and scientific changes to society. But she mourned the early death of her consort Prince Albert in 1861 for the rest of her life.

Princess Elizabeth became Queen Elizabeth II when she was 25 on the death of her father King George VI on February 6, 1952. Like Victoria, she has acted as a figure of continuity as the country has modernised.

She has served, with Philip at her side, through the 20th century and into the 21st century, witnessing technological advances and a succession of British governments of different political persuasions.

The Queen is also the first British monarch to have sent an e-mail and to have a message put on the moon

The Queen has become accustomed to countless milestones during her decades on the throne.

In December 2007, she became the longest living British monarch, overtaking Victoria who died when she was 81, and in May 2011 she became the second-longest reigning monarch in British history when she overtook George III.

The Queen after her coronation in Westminster on June 2, 1953. She is seen wearing the St Edward Crown and carrying the sceptre and the rod. Photo: PA Wire

According to Guinness World Records, the Queen also holds the world record for most currencies featuring the same individual.

The Queen is also the first British monarch to have sent an e-mail, to have a message put on the moon, have conducted a royal ‘walkabout’ and to have held a public concert in her back garden.

She is the second-longest serving monarch in the world after King Bhumibol Adulyadej of Thailand, who took to the throne in 1946 but who is now rarely seen in public.

The record of length of time on the throne can be calculated in different ways, but the Palace considers the total number of days plus hours and minutes to be the most accurate.

The Queen passes Victoria’s record at around 5.30pm today (6.30pm local time) 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.

10 facts you might not know about the Queen

• Although the Queen’s nickname is ‘Lilibet’, the Duke of Edinburgh is also known to affectionately call her ‘Cabbage’.

• The Queen loves horse racing but she never places a bet.

• She wakes to the sound of her personal bagpiper every morning and can even tell if someone different to her usual piper is playing.

• She does not have or need a passport as British passports are issued in her name.

• Before every state banquet, the Queen personally inspects the grand horseshoe-shaped table which is laden with ornate candelabra and historic dinner services in the Buckingham Palace ballroom to make sure it looks perfect for her guests.

• The Queen and her family like to play games in the evening at Balmoral – including the so-called Post-it note game when they write famous names on pieces of paper, draw them from a hat, stick them on their foreheads and try to guess which person they are.

• When the Prince of Wales married Lady Diana Spencer in 1981, the Queen was said to be so happy she did a little jig of excitement as she left the reception.

• She drinks Earl Grey tea and also likes a gin and Dubonnet immediately before lunch.

• She could have married the Duke of Edinburgh when she was 17 – the age of his first formal request to be considered as a suitor – but her parents thought she was too young. They wed when Princess Elizabeth was 21 and have been married for nearly 68 years.

• The Queen was once seen throwing a pair of tennis shoes and a racquet at Philip in frustration during an Australian tour. The spat was caught on camera but the footage was given to the Queen and never broadcast.