Two families asked the High Court to force the NHS to treat their children, who are dying from vCJD.

On Tuesday, the High Court gave doctors permission to use the treatment - but the hospital involved is still refusing to go ahead.

BBC News Online explains the background to this extraordinary case.

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Who has brought the case and why?

The parents organised the case on behalf of two teenage children, who are dying from vCJD.

The case has been brought because the NHS decided not to allow a controversial treatment aimed at slowing the progress of this disease to proceed in this country.

What form does the treatment take?

The treatment is a drug called pentosan polysulphate.

This drug has been around for years, but has never been recommended as a drug to treat people with CJD.

In fact, although it has been used in the past as a treatment for bowel or bladder inflammation, it has no licence for any use on humans at the moment in the UK.

Some vets use it as an effective drug for arthritis in dogs!

Because vCJD affects the brain, any drug treatment for people already showing signs of the disease must reach that organ.

However, if an injection of pentosan was given to the body, the natural filter between the bloodstream and the brain would stop it entering.

So, in order for pentosan to have any chance of working, it must be injected directly into the brain itself.

So what happens now?

Although the High Court has given permission for the drug to be used, that is not the end of the story.

The hospital trust involved is still refusing to carry out the treatment, even though doctors there are willing.

This is their perogative: There is nothing yet in law which says they have to do it.

However the Department of Health, even though its official advisers do not endorse Pentosan, will now try to find an alternative venue.

If it does, then the operation will go ahead quickly.

It is a relatively simple procedure, to insert a catheter tube into the brain and perhaps a pump under the skin to deliver constant doses of Pentosan.

Neither of these is particularly risky to the patient - it is the drug which has raised the objections.

Why do experts think that pentosan has a chance of working?

Increasing evidence from animal and laboratory experiments suggests that pentosan seems to have the ability to latch onto "prions" - tiny body proteins which appear to be the cause of vCJD damage.

There is the suggestion that it may be able to actively transport these prions out of brain cells.

In animal studies, giving pentosan appeared to lengthen the incubation period of the disease.

Scientists say that pentosan is an established drug, and appears to be relatively non-toxic.

Of course, animal studies are not always a reliable indicator of success in humans, but scientists who support pentosan say there is enough evidence to justify its use in human patients, particularly those with advanced disease, for whom there is no alternative.

So what's the problem?

The trouble is that other scientists - and some of them fairly eminent in the field of vCJD - believe that it would be inappropriate to attempt this treatment, and quite possibly expose the patient to an unneccessary risk.

They say that not enough safety research has been done to support its use.

There are still concerns - although hotly disputed - about the likely toxicity of the drug in the brain

So what is the central issue in the case?

It appears to be whether the existing research is strong enough to justify such a step into the unknown.

The life expectancy of both patients is short - and the parents would argue that, even if the injections were to cause some harm, which they firmly believe they will not happen, that risk is acceptable given that their very lives are at stake.

They argue that it is not the place of hospitals or health departments to obstruct a doctor when he wants to administer a treatment to a patient.