A man was critically ill in hospital with suspected rabies last night in what looks likely to be the first time the disease has been acquired by a human in Britain for a century.

Doctors treating the man suspect he contracted the rare disease after being bitten by a rabid bat. Although they are awaiting the results of laboratory tests, the doctors said his symptoms were consistent with rabies and he was being treated in an isolation ward.

The man, who has not been named, is a volunteer worker who helps with the conservation of bats in Angus. It is understood he was not immunised against rabies and it is feared he contracted the disease from a bat infected with the European bat lyssavirus (EBL) strain.

Doctors fear he has the rarer paralytic form of rabies, where paralysis begins in the feet before travelling through the rest of the body until it reaches the head. There is no effective treatment for the disease and it is almost always fatal. The man was "critical but stable" in the intensive care unit of Ninewells hospital, Dundee, yesterday, but it is understood his illness is at an advanced stage.

Drew Walker, director of public health at NHS Tayside, said there was minimal risk to the general public from rabies. "The only danger to the general public is if they handle bats. For some time now the advice has been for the general public to avoid handling bats in all circumstances. We can only reiterate that now," he added.

Only last month the government warned British bats may carry the EBL rabies strain. Although it is relatively common in some northern European countries, it is extremely rare in Britain. There have been only two known cases of bats with the disease here.

Bats can infect humans with rabies but there have been no known cases of them infecting other animals.

Similarly, humans have never been known to pass rabies among one another.

Despite this, there is a theoretical risk that those working with the man could contract the disease and they have been issued with protective clothing and precautionary immunisation has been offered to hospital workers and the man's family.

It is understood the man came to the hospital less than a month ago complaining of fever and mild neurological symptoms. But Dilip Nathwani, a consultant in infectious diseases, said he was now extremely ill from what he suspected was the paralytic form of rabies.

Dr Nathwani said the results of blood tests were expected today, but rabies was an extremely difficult disease to diagnose and even if the tests are negative the man may still be infected.

The man had many years' experience working with bats and Scottish Natural Heritage (SNH), the body which regulates who works with the animals north of the border, recommends that all bat workers are immunised. The vaccination is 100% effective.

Rabies can also be prevented after a bite from an infected animal if the vaccine is administered.

Colin Galbraith, chief scientist at SNH, said investigations into where and when the man was bitten were currently underway. The task is complicated by the varying incubation periods for the disease: he could have been bitten up to two years ago, although he is more likely to have been infected in the last few months.

In September, a woman in Lancashire was bitten by a rabid Daubenton's bat but did not develop the disease. Before that a pregnant woman in 1996 is the last person known to have been bitten by an infected bat in Britain. She, too, did not develop the disease.