Patients are being urged not to donate blood or organs

The patients from Addenbrooke's Hospital in Cambridge are among 4,000 in the UK who are receiving letters warning them of the risk.

The patients may have received blood products from donors who subsequently developed vCJD.

But experts stress the risk is very low, and relates to people who were exposed to blood products before 1999.

No test

Addenbrooke's is the regional centre for haemophilia and sees patients from all across East Anglia.

There is no test for the brain wasting disease so those at risk have no way of knowing whether they have vCJD.

The exercise was carried out by the Health Protection Agency and the advice issued on Tuesday was based on recommendations by the expert CJD Incidents Panel.

Professor Don Jeffries, from the CJD Incidents Panel, said they had come to the conclusion that they should take the precautionary measure in the interest of public safety.