Dr Geoff Hackett, a sexual health specialist at Good Hope Hospital in Birmingham, said patients are sometimes being inappropriately prescribed expensive drugs which do not effectively tackle their problem.

More than half of patients taking Viagra found it did not solve their problems adequately, he said, adding that low testosterone was the main problem for one in 10 men suffering erectile dysfunction and drugs like Viagra had no effect if taken alone.

"The biggest waste (of money) is a tablet that doesn't work," he said.

The NHS spends around 58m a year on 17 million repeat prescriptions for Viagra and other impotence drugs.

Dr Hackett tests the testosterone levels of all men who visit his clinic and some react angrily to being told they have wasted five years and lots of money taking pills that will not work for them.

"I have had some people say I'm going back to that surgery and asking for my money back," he said.

The doctor said low testosterone is a contributory factor for a further one in five (20 per cent) of men suffering sexual problems.

Dr Hackett, speaking at a BSSM briefing in central London, said erectile dysfunction is already recognised as an early warning of coronary artery issues and routinely asking men about it could help to identify people with potential heart problems.