Britain's Queen Elizabeth II, Prince Philip watch the proceedings from the royal barge during the Diamond Jubilee Pageant on the River Thames in London.

London -

Queen Elizabeth II's 91-year-old husband Prince Philip, who is in hospital with a bladder infection, is responding well to treatment, Buckingham Palace said on Thursday.

“It is unclear when he will be discharged, but he is likely to remain in hospital for a few more days,” the palace added in a statement.

Philip was taken by ambulance to hospital in the Scottish city of Aberdeen on Wednesday following a recurrence of the bladder infection that laid him low during the queen's diamond jubilee celebrations in June.

It is the prince's third health scare in the space of eight months, after he suffered a blocked coronary artery over Christmas last year which required the insertion of a stent.

He and the queen were staying at the royal family's residence at Balmoral in northeast Scotland when he was taken ill and driven to Aberdeen Royal Infirmary, about 40 miles (60 kilometres) away.

Buckingham Palace said on Wednesday that he was hospitalised as a “precautionary measure”.

Philip, whose official title is the Duke of Edinburgh, had appeared in good health on Monday as he carried out public engagements on the Isle of Wight, off southern England.

He had also attended several events at the London Olympics, and appeared delighted as he watched his granddaughter Zara Phillips, who went on to win a silver medal in the equestrian events.

But age has begun to take its toll. He spent five nights in hospital with a bladder infection in June, forcing him to miss the end of the huge diamond jubilee celebrations marking the queen's 60th year on the throne.

The infection came after he spent several hours standing on a royal barge in heavy rain as part of a jubilee pageant on the River Thames.

A few days before Christmas he was flown by helicopter to hospital for surgery on a blocked coronary artery after suffering chest pains.

Greek-born Philip is the longest-serving royal consort in British history, and has been the queen's stalwart companion throughout her reign.

He is famous for his politically incorrect jokes, but behind the scenes is said to be a key source of support for the queen who describes him as her “strength and stay”. - Sapa-AFP