The King's Fund wants a national debate on rationing which involves the public both as patients and as citizens who pay taxes.

"The NHS and the government should value the people who use and pay for the health service. They should be partners," said a spokesman.

He said this could involve taking some aspects of citizens' juries - panels of local citizens who decide on community issues - and adapting them.

For example, giving people more information about the arguments over rationing before a debate at a health authority meeting.

Alternatively, health panels or polls could be used for new expensive drugs.

Internet information

The charity also wants patients to be more involved in deciding which treatments they receive.

The Internet could provide information on the illnesses the drugs treat.

And interactive videos about diseases would allow patients to choose the information which was immediately relevant to them.

Videos already exist for some conditions, such as prostate cancer.

Another way of involving patients more is to give them a greater role in clinical trials.

The first national clinical trial designed jointly by patients and doctors is due to start soon.

It will look at the effect of taking HRT on women being treated for breast cancer.

The idea of joint trials is that patients will be given more information on the kind of drugs they are taking and give them more control.

They may, for example, ensure the results place more emphasis on patients' personal experience of the drugs, such as side effects.

Instant cures

Viagra is just the first of a wave of new so-called "lifestyle" drugs which could be prime targets for rationing.

They include anti-obesity treatment orlistat and anti-anxiety drug seroxat - dubbed the pill for shy people.

Media hype suggests the pills are instant cures for a range of conditions which form the basis of most of our current neuroses.

There is concern that demand may push the NHS budget to breaking point, although most should only be prescribed to those with a clinically defined need.

In the case of impotence - which reportedly affects one in 10 men in the UK, there are at least two other drugs coming up which could prove rivals to Viagra.

They are Vasomax and apomorphine.

Vasomax, marketed by US-based Schering-Plough, is reported to work up to twice as fast as Viagra and to have fewer side effects.

Viagra takes between 20 minutes and an hour to kick into action.

Unlike Viagra, Vasomax does not apparently interact with nitrate-based drugs and does not cause vision problems.

Vasomax is on the market in Mexico as Z-Max

Viagra's manufacturer Pfizer warns against mixing Viagra with nitrates because it could lower blood pressure to life-threatening levels.

Vasomax's side effects include headaches and blushing.

The drug is already licensed for use in Mexico, under the name Z-max.

It could be on the market in Europe by April.

Vasomax works by blocking the nerves in the penis, allowing blood to flow in and produce an erection.

It is reported to be up to 45% successful in improving impotence in men, depending on the dosage.

Hypertension

Apomorphine was formerly a treatment for hypertension - like Viagra.

It is being tested by US-based TAP Holdings and is said to have a success rate of up to 60%.

But trials did not include men with known physical causes of impotence.

Side effects include nausea in up to 39% of patients, depending on the dosage.

It works by stimulating the neurological signals which create an erection.

Neither drug is not thought to be as effective as Viagra, but doctors say it will allow impotent men to have a wider range of options for treatment.