Families of teenagers struck down by the human form of BSE have been given permission by the high court to seek an untried treatment for the fatal condition.

Dame Elizabeth Butler-Sloss, president of the family division, said doctors could use the drug pentosan polysulphate, but a hospital trust is still refusing to allow a neurosurgeon to inject it into the brains of two young people in the hope that it might stop further brain damage.

The Department of Health is investigating whether other hospitals might be prepared to allow the treatment to take place. Its advisers have so far refused to recommend the use of pentosan to fight variant CJD, the incurable disease that has killed 119 Britons and left 10 more facing death.

There is no approved treatment, although the govern ment has allowed patients who have doctors' permission to take quinacrine, which has been used against malaria and internal parasites.

Pentosan is employed in the US and Germany against inflammation of the bladder and its supporters say animal experiments suggest it could work against the rogue prion proteins that are thought to be a key factor in the development of vCJD. The treatment is about to be given to patients suffering a different form of CJD in Japan.

The case involved the families of Belfast student Jonathan Simms, 18, and a 16-year-old girl who cannot be identified. It was heard in private but the judgment, delivered to the families of the patients last Wednesday, was made public yesterday.

Jonathan's father Don said: "This is about helping our boy as soon as possible. It is our last chance. We regard this treatment as experimental but it is not experiment for experiment's sake. The fact is there is nothing available on the horizon at present. We think this treatment has potential, but no one knows how much."

Dame Elizabeth said both patients were now helpless and confined to bed. Mr Simms had been realistic about the prospects of success. He realised the treatment might not work and even if it did his son would remain severely brain damaged. The girl's parents would be content if treatment prolonged her life in her present condition and slowed the course of the disease.

Dame Elizabeth ruled the treatment would be lawful and in the best interests of the patients. She said: "Although this cannot be a research project , there would be an opportunity to learn, for the first time, the possible effect of PPS [pentosan] on patients with the treatment about to be given to patients in Japan."