Britain’s Princess Anne has returned to official engagements, less than three weeks after she needed hospital treatment for concussion sustained from a head injury believed to have been caused by a horse.

Anne, 73, the younger sister of King Charles and the late Queen Elizabeth’s only daughter, spent five nights in hospital after suffering what Buckingham Palace said was a minor head injury on June 23.

WATCH THE VIDEO ABOVE: Princess Anne back at work after head injury.

Know the news with the 7NEWS app: Download today

It meant she was forced to postpone her planned engagements, including a trip to Canada.

However, on Friday the princess, often credited with being the hardest-working member of the royal family, returned to duties, attending the Riding for the Disabled Association National Championships held in western England.

The horse-loving royal, who was an Olympic equestrian herself, has been a patron of the charity for more than five decades and its president since 1986.

Anne suffered her head injury while walking in the grounds of Gatcombe Park estate where her home is located.

It is thought the concussion was caused by an impact from a horse’s head or legs, although a royal source said she had been unable to recall what happened.