THE Duke of Edinburgh was admitted to hospital last night after taking ill at the Queen's royal retreat at Balmoral.

The 91-year-old, who has been treated in hospital three times in the last eight months, was taken to Aberdeen Royal Infirmary after suffering a recurrence of the bladder infection he contracted in the summer.

A Buckingham Palace spokesman said he was admitted as a precautionary measure but is likely to remain there over the next few days for further investigations and treatment.

He was taken by ambulance, travelling 40 miles from the castle, near Ballater, Aberdeenshire, the Palace added.

It follows a similar admission in May this year when he took ill after standing in the rain for a long period of time as he watched the Queen's Diamond Jubilee pageant on the River Thames.

He spent five days convalescing at central London's Edward VII hospital but doctors said there was no cause to be unduly concerned about the infection at that time.

A Buckingham Palace spokesman said yesterday: "The Duke of Edinburgh was taken to Aberdeen Royal Infirmary as a precautionary measure.

"He has had a recurrence of the bladder infection that he had in the summer and has been admitted to hospital for investigation and treatment. His Royal Highness is likely to remain there for the next few days."

The Duke and the Queen were enjoying a break at Balmoral after attending a number of Olympic events in London.

He was at the Queen's side during the opening ceremony and the following day when they toured the Olympic Park.

He then watched his granddaughter Zara Phillips's Olympic equestrian debut and was at the ExCel exhibition centre a few days later to watch the boxing.

The spokesman added: "He has been resident at the castle for a short while but he has also undertaken engagements on the Isle of Wight."

Prince Philip appeared to be in good spirits as he took part in Cowes Week on the island over the last few days in his role as Admiral and member of the Royal Yacht Squadron.

He watched the racing in Solent on Tuesday and attended a number of luncheons before falling ill yesterday afternoon.

His latest admission follows a heart scare over Christmas last year which saw him admitted to Papworth Hospital in Cambridge with chest pains on December 23.

He was at the hospital for four nights following a "minimally invasive procedure of coronary stenting" and was not able to attend the Royal Family's annual Boxing Day shoot, which he normally leads.

Prior to these health problems, the Duke's most recent illness was an uncharacteristic cold in October that forced him to pull out of an overnight stay in Italy.

Despite his age, he still undertakes around 350 engagements a year and last year undertook two foreign tours with his wife – to Australia and Ireland.

He is next due to appear in public when he accompanies the Queen to the opening ceremony of the London 2012 Paralympics on August 29.

It is customary for the royal couple to spend several weeks on their Balmoral estate every August and September.

It is not known if other members of the royal family, including the Princess Royal, whose birthday it was today, were also staying at Balmoral.

A Buckingham Palace spokesman said: "It is usual for other members of the royal family to be in residence at Balmoral with the Queen during the summer period but we do not know who would be there."