The Duke of Edinburgh is likely to have an underlying cause of his bladder infection and there is little he can do personally to ease the condition, an expert has said.

Malcolm VandenBurg, a specialist in general medicine and male health problems, said there could be numerous causes for the recurrence.

The consultant said there were three more likely causes: an enlargement of the prostate gland, cancer in the prostate or an infection in the actual prostate.

He said: “If a man gets a bladder infection it is usually associated with something else going wrong.

“With a man of Prince Philip’s age one would immediately think that he had some obstruction to the flow of his urine...

“The thing most likely to be in a man of his age is going to be some enlargement of the prostate.”

Dr VandenBurg said with age the bladder loses its tone completely ­– “it is like a floppy balloon”.

The bladder does not expel all the urine present which increases the chance of an infection.

Prince Philip’s “exceptional medical team” would also be studying if there was something else making the body prone to infection, such as diabetes, the doctor said.

If the duke’s medical team did not establish the precise cause of his original infection they will now ensure they do, said Dr VandenBurg.

An inherent medical disease could be treated with drugs to reduce the prostate’s size but Prince Philip’s surgeons will be loath to operate, Dr VandenBurg said.

The consultant stressed elderly patients’ ability to ward off infections is lesser than young people’s.

Eileen Burns, from the British Geriatrics Society, was asked by the BBC why the duke’s bladder infection may have come back.

She said: “I think there are a number of possible reasons. Bladder infections are quite common anyway so it may just be bad luck.”

Other explanations, Dr Burns said, included that immune systems in older people are less vigorous and that sometimes there can be an abnormality within the urinary tract. Stones within the bladder were another possible cause of infection, she added.

Roger Kirby, a consultant urologist and director of The Prostate Centre in central London, told the BBC: “As you get older your resistance to any infection becomes less. It is harder to clear them up in people of that age and the immune systems don’t work that well.”

He said the duke may have gone into hospital so he could be given “more powerful” intravenous antibiotics to clear up the infection.

He said: “I think within a few days, hopefully, the antibiotics will work and the patient should make a rapid recovery and all will be well. I don’t think this is a drama.

“This is not at all unusual...”

He added that the duke had been looking “pretty sprightly” at recent events and would hopefully recover with the right antibiotics.