Scientists hope they have identified the bug responsible for worldwide health warnings linked to a virulent form of pneumonia.

The World Health Organisation believes the discovery of a virus from the family responsible for mumps and measles could represent an important breakthrough in the battle against a condition blamed for killing up to 10 people and laying low hundreds of others.

The only British victim so far suspected of suffering from severe acute respiratory syndrome was identified yesterday as Nigel Glassey, 64. He is being treated at North Manchester hospital where his condition was said to be much improved. Mr Glassey returned from Hong Kong, at the centre of the crisis, at the weekend. A suspected case has been reported in Dublin.

Evidence of a virus, which appears to be a previously unidentified member of the paramyxovirus family, was identified by German researchers on Monday. Within hours researchers in Hong Kong had found evidence in three patients.

David Heymann, the executive director of communicable diseases at the WHO, told the BBC: "We have some good clues now. Next, what is necessary is to find out what kind of virus [it is] and that will take some time in laboratories, but they are already working on that."

Dick Thompson, a WHO spokesman, said: "We have not identified this as the cause of the outbreak. That will take some time, I don't know how much."

He understood that the Hong Kong scientists had not found evidence of the virus in most samples they studied. Patients might be carrying infections from more than one cause. "It is possible this is the agent. We just need to do more work."