• Age: about 10 per cent of men are affected to some extent by the age of 40, rising to almost 60 per cent of those over 70.
• Narrowing or hardening of the arteries: high cholesterol and high blood pressure are possible early signs.
• Diabetes: damages fine arteries.
• Hormonal imbalance, such as low testosterone.
• Side effects of drugs that disrupt nerve impulses to penile tissue, including high blood pressure drugs and antidepressants.
• Nerve damage, caused by trauma, major pelvic surgery and diseases such as multiple sclerosis.
• Heavy smoking, which affects circulation in small arteries.
• Long-term alcohol abuse, which can affect the nervous system, and drug abuse.

Psychological

Performance anxiety, guilt and depression. If the sufferer has early-morning erections and is able to masturbate successfully, the cause is most likely to be psychological.

How can impotence be treated?

Drugs

Monthly prescriptions have more than doubled since March 2000 to 27,568 last month. Side effects of anti-impotence drugs include nausea, vomiting, flushing and dizziness.

• Viagra (sildenafil): the effects last for a few hours and the drug works by relaxing muscle and increasing blood flow to the penis. Men with heart disease can take it safely, but not if taking nitrates to relieve angina. Nitrates have similar effects and could seriously lower blood flow in the heart.
• Cialis (tadalafil): launched earlier this year, it acts similarly, but lasts for at least 24 hours. Some men prefer to choose the day, rather than the hour, when action is required.
• Levitra (vardenafil): the most recent, also acts speedily to increase local blood flow with an optimum effect for up to five hours.
• Uprima (apomorphine): produces an erection within 20 minutes, but has a different action and can, unlike the other drugs, be used by men who take nitrates.
• Injectables: there are several self-administered systems, including Caverject, Viridal Duo and Muse, which are options if drugs taken orally do not work. These work within 30 minutes and last for about one hour.

Surgery

A last resort where disease or injury has led to major damage. Implants and inflatable penile prostheses are basically fluid-filled, flexible cylinders. The surgeon also inserts a discreet hand pump into one testicle.

Improving general health Stopping smoking, losing weight and cutting back on alcohol can all help.

Alternative remedies

"There are many herbal remedies and supplements advertised, but no widely accepted evidence that they work," says Mr Whittlestone. With some, there could be a large placebo effect and he would not discount that. Ginkgo biloba, said to stimulate circulation, and ginseng, a stimulant, are among the most popular.