The Duke of Edinburgh is expected to stay in hospital for a few more days while receiving treatment relating to a “pre-existing condition”.

His planned admission on Friday to King Edward VII’s Hospital in central London, which has treated members of the royal family for decades, was described as precautionary by Buckingham Palace.

According to reports, the move follows a spell of ill-health. The Sun quoted a royal source as saying that the 98-year-old duke had had a fall recently, while the Mail reported he had been battling a flu-like condition.

Uniformed police officers were standing guard outside the hospital entrance on Saturday morning alongside a doorman in a top hat, while camera crews set up across the road.

The duke’s condition is not considered serious enough for the Queen to change her schedule. She left Buckingham Palace for Norfolk by train on Friday, to begin her traditional festive break on the Sandringham estate, where the duke has spent much of his time since retiring from public duties in 2017.

The duke has generally enjoyed good health, appearing to recover well from a hip replacement operation in April 2018. He escaped with minor injuries after a dramatic car crash near Sandringham last January, but in the past decade has been admitted to hospital for abdominal surgery, bladder infections and a blocked coronary artery.

When the duke was admitted to hospital on Friday, Buckingham Palace said in a statement: “The Duke of Edinburgh travelled from Norfolk this morning to King Edward VII’s Hospital in London for observation and treatment in relation to a pre-existing condition. The admission is a precautionary measure, on the advice of His Royal Highness’s doctor. The duke was not taken by ambulance and is expected to be in hospital for a few days.”

Last Christmas, the duke missed the royals’ traditional Christmas Day trip to church. An advocate of healthy eating combined with exercise, the duke once said that he largely followed the low-carb Atkins diet, and drank only moderately.