Members of the CJD Surveillance Unit have told the BSE inquiry that they are in the dark about the effects of new variant CJD (Creutzfeldt-Jakob Disease) which has already killed 25 people.

30 year incubation period

Speaking at the inquiry on Wednesday, Simon Cousens, an epidemiologist for the unit, said it was impossible to know how many deaths there would be because the incubation period for the disease could be more than 30 years.

He said: "At the moment it's really not possible to say whether there might be few more than a dozen or up to 100 or many thousands."

In a statement to the inquiry, the unit's leader Dr James Ironside made clear that the body was set up in 1991 specifically to look for evidence of BSE affecting people, despite government assurances at the time that beef was safe to eat.

Younger victims provided a clue

But fears were prompted in 1995 when people under the age of 45 died from CJD - a disease which usually affects mainly the elderly.

The unit belives that no cases have gone undetected

Although brain examinations showed what appeared to be a new variant of CJD, no immediate link was drawn, the inquiry was told.

Ten cases were identified before the government made an announcement about nvCJD in March 1996, sparking the beef crisis.

Analysis of the nvCJD showed the average age of the victims was 29, compared with 66 for "classical CJD".

But the specific causes of nvCJD still baffled the team, the inquiry was told.

'Distribution of cases appears to be random'

Despite clusters of the disease in Kent, Mr Cousens said: "The geographical distribution appears to be random. There is absolutely no evidence that cases lived closer to rendering plants than the general population."

Although the team said there was "very powerful" evidence that BSE caused nvCJD, Mr Cousens added that he was not convinced young people were more at risk because they were more likely to eat hamburgers and kebabs than the elderly.

"Personally, I'm not convinced that the gradient in exposure is sufficiently strong to explain a complete absence of cases of people aged over 53. It's still a bit of a mystery," he said.

The team said they believed no cases had slipped through the net before the new form of the disease was identified.