The occasion has been marked by the release of a picture showing her indulging her passion for horses and ponies.

Standing with two of her Fell ponies, the Queen was photographed as the build-up begins for the Royal Windsor Horse Show, which commissioned the image.

Queen hailed as ‘inspiration to so many’ on 96th birthday. (PA)

Meanwhile the royal family have paid tribute to Britain's longest-serving monarch in a string of social media post where her majesty was hailed an “inspiration to so many across the UK”.

The official Twitter account of the Duke and Duchess of Cambridge tweeted a picture of William and Kate with the Queen at the Chelsea Flower Show a few years ago and another image of the monarch and the Duke of Edinburgh surrounded by their great-grandchildren.

The message read: “Wishing Her Majesty The Queen a very happy 96th birthday today!

“An inspiration to so many across the UK, the Commonwealth and the world, it’s particularly special to be celebrating in this #PlatinumJubilee year.”

The official Twitter account of the British monarchy also recognised the Queen’s milestone with a black and white photograph of the then Princess Elizabeth.

The tribute read: “Happy Birthday Your Majesty!

“Today as The Queen turns 96, we’re sharing this photograph of the young Princess Elizabeth aged 2.

“Then, in 1928, it was never expected she would be Queen, and this year Her Majesty is celebrating her #PlatinumJubilee – a first in British history.”

The Queen travelled from Windsor to her Sandringham estate on Wednesday to stay at a property loved by her late husband, the Duke of Edinburgh, for her birthday.

She has already received birthday wishes from Prime Minister Boris Johnson and Labour leader Sir Keir Starmer and gun salutes will be fired in her honour later on Thursday.

This year, the Royal Windsor Horse Show will mark the Platinum Jubilee with A Gallop Through History, an equestrian display showcasing horses from across the globe.

It has been billed as a “personal tribute to our monarchy” and will feature more than 500 horses and more than a thousand performers taking the audience on a journey from Elizabeth I to the Queen.

The new photograph of the Queen was taken in March in the grounds of Windsor Castle by Henry Dallal, who was also commissioned to take an official portrait of her to mark her 90th birthday.

On the Queen’s left is the pony Bybeck Nightingale and on her right is Bybeck Katie. Both animals will feature in A Gallop Through History.

Her Majesty’s love for the equine world is something she shared with her mother, and she has been breeding and racing horses for more than 60 years.