Six thousand Britons are to be told they may have been exposed to the human form of mad cow disease through blood products, the government said on Tuesday.

Sir Liam Donaldson, Britain’s chief medical officer, told a news conference that the risk of people developing the deadly degenerative brain disease was very small but the government was taking a “highly precautionary” approach.

He said a risk assessment identified people who may be at a small increased risk of developing vCJD than the rest of the population who ate beef during the 1980s and 1990s.

“This information will enable these people and their doctors to take the necessary steps to minimize the risk of onward transmission of vCJD,” Donaldson said.

Blood products, such as clotting agents to treat bleeding disorders, are made from donated blood.

Variant CJD is the human equivalent of bovine spongiform encephalopathy (BSE), or mad cow disease, which is linked to eating meat infected with BSE.

Two cases of suspected transmission of the infectous agent through a blood transfusion have been reported. Both patients received blood from donors who were later identified as being infected.

Britain banned people who have had transfusions in the past two decades from donating blood after the first case was reported.

“The risk to any individual is very small indeed,” Professor Lindsey Davies, an expert on the disease at the department of health, told Sky television.

“We just want to take a public health precaution to insure people who might have received a lot of these products don’t, for example, give organs for transplant and do alert their doctors when they are being treated so we can be sure there is no further increased risk of transmission.”

Britain took several measures to insure the safety of its blood supplies in the late 1990s.