TOWARDS the end of his life Johannes Brahms composed a mournful series of songs known as the Five Lieder, Op 94. The philosopher Nietzsche is said to have quipped that Brahms's inspiration must have been 'the melancholy of impotence'.

Nietzsche's remark, if he made it, was in exceptionally poor taste. The fact is, most men would never call another man impotent, even in jest: the whole subject of impotence - the inability to achieve or sustain an erection - is just too sensitive and embarrassing.

'For most men, it's catastrophic if their sex life drops off,' says agony aunt Virginia Ironside, who receives many letters about impotence from men and women. 'They feel if they're not potent they don't exist.'

Many men are unwilling to approach their GPs about the problem. One middle-aged sufferer, Jack, wouldn't go to his doctor because he was an old school friend. 'Besides,' he says, unconvincingly, 'he's got a lot of other people who've got real problems.' So Jack took his complaint to the place where men who have money, and who can't face tackling the National Health system, tend to go: a private impotence clinic.

A current newspaper advertisement for the Grosvenor Clinic - the north London clinic that treated Jack - reads: 'Impotence: Erectile Problems. Contrary to popular belief, this common yet distressing problem is very rarely of psychological origin. Our specialist team of expert doctors and surgeons first diagnose the actual physical cause of the problem, then offer the appropriate treatment . . . ' But what exactly is the 'appropriate' treatment for impotence?

Until 10 or 15 years ago it was assumed that most impotence was psychological - and that psychotherapy was the only treatment. Then it was discovered that a plant-based drug called papaverine, which is used to make blood vessels dilate, could be injected into the penis to produce an erection. (Once the erection is achieved, the man can ejaculate as normal.) For the first time, doctors realised, they had a reliable physical treatment.

Men want the problem to be physical. This places it in the same realm as a hernia or high blood pressure, something for which you can go along and get a remedy - something for which you can't be blamed. The private clinics tend to emphasise the likelihood of a physical cause. 'The number of patients in whom the cause is psychological is next to none,' insists Dudley Rogg, director of the Grosvenor Clinic. 'There's almost always some physical problem.'

Consequently, Jack was not referred to a counsellor or psychotherapist at the Grosvenor Clinic, even though he was found to be in perfect health. ('But then', he maintains, 'I don't have any mental hang-ups'.) Instead, the treatment he received was a course of injections - which, Mr Rogg says, is the clinic's single most common form of treatment. This means Jack has to inject his penis with the drug each time he wants to have sex. It sounds like a desperate remedy, but worse, even, than the physical discomfort must be the realisation that sex can never be spontaneous: it can only take place at around 15 minutes' notice (the time the drug needs to take effect).

Jack was told that the valves in his blood supply system had simply 'got a little sticky'. The idea of the injections was that they would 'loosen up the valves'. Jack's course, which he is now part-way through, consists of eight injections, costing pounds 100 on top of his initial consultation fee of pounds 260. By the end, he expects that he will be having sex unaided - 'flying solo,' Mr Rogg calls it.

Gordon Williams, a urologist at the Hammersmith Hospital in West London, and an impotence expert, questions this theory. 'Treatment by injection is just producing an erection.' In tests he conducted, he found that only about seven per cent of patients could be 'kick-started' in this way. Like many other specialists, Mr Williams believes the physical or organic causes of impotence are being overstated. 'Almost all men with impotence have a psychological element. Fifty per cent don't have any organic cause.'

So if injections cannot provide a permanent solution to impotence, what can? The most extreme remedy is the penile implant, an artificial stiffening device that is inserted surgically into the penis. There are several different kinds - including the 'rigid' and the 'inflatable' - and once they are inserted, they are not normally removed.

This was a step Peter, another despairing middle-aged sufferer, was prepared to take. Implants, like injections, are in certain circumstances available on the National Health (a fact that may come as a surprise to some patients who have gone to private clinics). So although Peter couldn't afford private fees, an implant could be obtained through his local hospital. The trouble was, for reasons of cost, the hospital could only supply a rigid silicone implant.

A rigid implant can be bent up for use and down for concealment - but once implanted, the size of the penis does not alter. 'It did not appeal to me one bit,' says Peter. 'I felt it would look unnatural.' So he too was left to fall back on the injections, which he hates: 'Making love by appointment,' he calls it. His doctor suggested that as he got older he wouldn't want to make love so much - 'A load of bloody rubbish,' says Peter, angrily.

Some estimates report that at least one in 10 men has continuing or chronic impotence. But for obvious reasons, it wasn't easy finding sufferers to interview for this article. Of those I spoke to, Peter was the most desperate. 'You're talking to people who are not even complete men,' he told me. 'To tell you the truth, I'm about to crack up.' Yet for all his desperation, the only other people Peter has spoken to, apart from his wife, are his GP and some hospital doctors: 'I can't talk to friends and colleagues,' he says. 'A man does not want to seen to be less of a man than he should be.' All the advances in treatment of impotence over recent years have not even begun to break down the taboo which surrounds it.

Jack and Peter are not real names.

(Photograph omitted)