But the landmark date this weekend will see little fanfare, as the 95-year-old monarch traditionally spends the anniversary of the death of her father in private.

The sovereign's record-breaking reign as head of state began when she was aged 25 and watching wildlife in a remote part of Kenya with her husband, Prince Philip.

She has since become the one constant in an era of rapid social and political change, a figurehead of modern Britain and a living link to its post-war and imperial past.

The Queen -- who regularly tops surveys as the most popular royal -- on January 23 flew by helicopter to her sprawling Sandringham estate in eastern England.

She had been due to stay at Sandringham House with close family over Christmas and the New Year but the annual visit was postponed because of surging cases of Omicron.

No public engagements are expected on Sunday, in keeping with previous years.

But four days of festivities are planned for early June, including a military parade and a music concert, street parties, a mass attendance picnic and a "Platinum Pudding Competition".

Commemorative coins have been minted to mark the unprecedented milestone.

Retreat

At Sandringham, the queen is staying at Wood Farm, a five-bedroom cottage that was favoured by her late husband after he retired from public life in 2017.

According to British media, Prince Philip spent his time there reading, painting and walking, in more modest surroundings away from liveried servants and royal pomp.

The queen travelled to Sandringham by helicopter and was photographed in the back of a Range Rover, wearing a silk headscarf printed with birds.

The 20,000-acre (8,100-hectare) estate, near the north Norfolk coast, is dear to her heart.

Not only was it a retreat for Philip until he joined her in Covid isolation at Windsor Castle in 2020, but also for her father, George VI, who died there of lung cancer, aged 56.

It was also a favoured residence for her grandfather, King George V, who also died there, and her great-grandmother, Queen Alexandra.

After Philip's death in April last year, the queen returned to public and official engagements, including hosting world leaders at the G7 summit in Cornwall, southwest England.

But she has been forced to slow down on advice from doctors, after an overnight hospital stay in October sparked public concern.

Since then she has largely stayed at Windsor and made few public appearances.

The last dates back more than a month to her annual -- recorded -- Christmas message, where she paid a rare personal tribute to her husband of 73 years and his "mischievous inquiring twinkle".

Respite

Only three monarchs in global history have reigned for more than 70 years.

France's Louis XIV reigned for 72 years, 110 days from 1643 to 1715. Thailand's king Bhumibol Adulyadej was on the throne for 70 years and 126 days from 1946 to 2016.

Johann II, prince of Liechtenstein, ruled for 70 years, 91 days from 1858 to 1929.

Sandringham could give Elizabeth some respite from a scandal involving her second and reportedly favourite son Prince Andrew that has cast a shadow over her jubilee year.

In mid-January, she stripped him of his honorary military titles and charitable positions as he battles a US civil case for sexual assault.

The move effectively removes him from public life, and is designed to insulate the royal family from any damaging revelations and repercussions.

Andrew, 61, vehemently denies the accusation but he has been tainted by his associations with the convicted sex offenders Jeffrey Epstein and Ghislaine Maxwell.