The Princess Royal, 73, sustained the injuries at the Gatcombe Park estate on Sunday evening and remains in Bristol’s Southmead Hospital as a “precautionary measure”. It is believed there were horses on the estate and the senior royal is likely to have sustained minor head wounds in an incident involving one of the horses.

"The Princess Royal has sustained minor injuries and concussion following an incident on the Gatcombe Park estate yesterday evening," the palace statement said.

"Her Royal Highness remains in Southmead Hospital, Bristol, as a precautionary measure for observation and is expected to make a full and swift recovery," it said.

"Her injury is consistent with an impact from a horse's head or legs," the BBC quoted sources as saying.

The King Charles has been kept closely informed and joins the whole royal family in sending his fondest love and well-wishes to the princess for a speedy recovery,” the statement said.

The palace stressed that Princess Anne, one of the senior-most working royals as the monarch's sister, is “recovering well” and is in a comfortable condition.

"On doctors’ advice, Her Royal Highness’s engagements for the week ahead will be postponed. Her Royal Highness sends her apologies to any who may be inconvenienced or disappointed as a result," it said, which implies a trip to Canada scheduled for the end of this week is now off.

The Princess will also be unable to attend tomorrow's state banquet organised by her brother in honour of Japanese Emperor Naruhito, who will be visiting the UK this week alongside his wife, Empress Masako.

Princess Anne was accompanied by her husband Sir Tim Laurence, daughter Zara Tindall and her brother Peter Phillips on the estate at the time. Laurence is said to have accompanied his wife to the hospital.

Princess Anne is known for her interest in horses and her achievements in equestrian sports. She was the first member of the Royal Family to compete in the Olympics, in the games in Montreal in 1976

As the second child of Elizabeth II and Prince Philip, she was third in line to the throne when she was born and she is now 17th in the line of succession.