Deputy Chief Medical Officer Jeremy Metters: It's precautionary"

Ministers made the announcement after a recommendation from SEAC - the body of experts who advise the government on BSE and its human equivalent, nvCJD.

The SEAC committee believe there is a 'theoretical risk', that the agent which causes nvCJD could be passed through blood products.

John Pattison: a prudent move

Their report, to be published officially in the next few weeks, calls for the introduction of leucodepletion - a process that removes white blood cells from donated blood.

Professor John Pattison, the chairman of SEAC said: "It is possible that there are a significant number of people who are incubating new-variant CDJ who will be blood donors, and if that is the case it seems prudent to take precautions to try to minimise the risk."

Government acknowledges danger

Frank Dobson, Secretary of State for Health, said: "We will do whatever we are advised to reduce the theoretical risk to the blood supply of the transmission of nvCJD.

"The National Blood Service has at my request been planning since November for the introduction of leucodepletion. They will now implement these plans. Although the risks are still theoretical, it is better to be safe than sorry."

The government has been keen to stress that there are no risks associated with donation of blood and has appealed to the public to continue making donations.

"If there is a risk from receiving blood transfusions it is a minute one, and people who need blood would be in infinitely greater danger of dying without a transfusion than from catching CJD," a health department spokesman said.

Foreign supplies

Another course of action that has been considered is a total ban on blood transfusions from donors in the UK.

Patient can donate blood before an operation and receives it back during surgery

But that would mean Britons would have to accept transfusions of foreign blood, which could have higher risks of other infections. It would also give the National Health Service (NHS) a massive bill as its British donations are free.

Claire Rayner, chair of the Patients' Association, called for greater use of autologous blood transfusions in which a patient donates blood before an operation and receives it back during surgery.

She said the practice was already used in the private sector but was not readily available in the NHS. She said it would help reduce some of the paranoia that seems to surround blood.