Once it was assumed that about 90 per cent of cases of male impotence, or erectile dysfunction as it is now called, resulted from psychological problems. We now know that the truth is nearer the opposite, that most cases of erectile difficulty are caused by illness, medication or injury, rather than the infinitely more vague 'loss of libido'.

Alcohol and smoking are well-known impotence inducers, but anti-hypertensive drugs and conditions such as diabetes can also result in difficulties. In fact, anything that results in a diminishing of arterial blood supply to the penis will make erections either difficult or impossible. For this reason, the problem is likely to get worse with age, and it is estimated that one-third of men in their sixties and half of those in their seventies experience erection problems.

In the past few men were willing to mention the problem to their doctor, or even admit it to themselves. Many believed they had no choice but to accept their situation as a natural part of the ageing process. Embarrassment on the part of both doctor and patient limited discussion.

Since the early Eighties, however, advances in research have resulted in more open discussion of impotence. A number of treatments, both mechanical and medical, have also become available to help overcome the problem.

The first drug aimed specifically at treating impotence was granted a licence in May. Caverject will relax muscles sufficiently to cause an instant erection when injected. Initially, the drug is injected by the GP, but patients can learn to administer it themselves.

Other, more established, drugs can result in unwanted side-effects, such as priapism, persistent and painful erections and drops in blood pressure, resulting in dizziness or, in some cases, fainting.

Dr Geoffrey Hackett, a GP and university lecturer who specialises in treating erectile problems, says Caverject offers the 'safest' treatment available. 'It breaks down in the bloodstream and does not cause priapism. It makes everything go back to normal - in fact, better than normal.

'Patients are delighted to have the return of the easy erections of their youth. Ejaculation happens completely naturally and the penis returns to its flaccid state afterwards.

'My own feeling is that drug treatment is better value for money and far more effective than hours and hours of psychosexual treatment.'

He believes impotence can almost always be overcome, given enough motivation on the part of the patient. 'When patients come to me with this problem the first thing we have to do is establish what is causing it. The most common causes of erectile failure are heavy smoking and drinking.

'Alcohol consumption over 40 units a week will cause at least a degree of impotence, and as a man gets older, this effect will increase. Then we have to look at any drugs the patient might be taking.

'Certain drugs for high blood pressure, particularly diuretics and beta-

blockers, which restrict blood supply to the extremities, will result in impotence, but hypertension itself is a major risk factor.

'For most men, impotence is a serious matter which can cause tremendous psychological and relationship problems. Yet nowadays, we can give erections back to every male patient who wishes it.'

But are men willing to inject themselves in such a sensitive area? 'Well, diabetics who take insulin have learnt to inject themselves,' Dr Hackett says. 'It all depends on how much the patient wants his potency restored. Also it can be related to how much his partner wants it. If his partner isn't bothered, he may not want to take that step.

'I find that 40 per cent of patients I teach continue to use this method. It all depends, to my mind, on how it is sold.'

A number of mechanical devices, such as implants and stiffeners that can be inserted into the penis, are also available. The devices, together with the operations to fit them, can cost up to pounds 3,000 and are more popular in the US than Britain.

Vacuum devices which draw blood into the penis are also offered, but are generally unpopular with patients because of the awkwardness of application.

If loss of erections occur through pelvic injury, vascular reconstructive surgery may be necessary. This can also restore potency.

But the first fact to establish is whether the problem is physically or psychologically based. If psychological problems are the cause, there will be night-time erections. If the problem is physical, however, there will be no erections at all.

In cases of psychological difficulty, a short course of a drug is usually prescribed to enable the body to begin working again on its own. Patients who are diabetic or taking antihypertensive drugs may have to use the drug on a permanent basis.

The absence of a 'quick cure' means most men fail to seek help, however. Dr Hackett says: 'So far, unfortunately, there are no simple tablets available, although there may be one day.'