Thousands of people have been banned from donating blood because of fears over vCJD. BBC News Online examines the move.
Other countries have also banned blood donations from Britons
What has been announced?
Health Secretary John Reid has announced that everybody who has received a blood transfusion in the UK since 1980 is to be banned from donating blood.
The ban, which will affect thousands of people, has been prompted by fears that the human form of BSE could be transmitted through contaminated blood.
The decision to include those who have had transfusions since 1980 is based on the premise that BSE did not emerge in the UK until after this date.
Can vCJD be transmitted through blood?
Scientists believe the risk of contracting vCJD through infected blood is very small.
The disease is believed to have killed 139 people in the UK since it emerged nine years ago. A further seven people with vCJD are still alive.
In December, Mr Reid announced the first possible case of transmission through contaminated blood.
He told MPs that an elderly man who received blood during an operation had subsequently died of vCJD.
The blood had been donated by a man who later went on to die from the disease.
While there was no proof that the two deaths were related, Mr Reid said a link could not be ruled out.
The Department of Health says 15 people received blood from donors who went on to develop vCJD.
None of these has yet displayed symptoms of having the disease.
Should people who have had transfusions be concerned?
The health secretary says the ban on collecting blood from people who have had transfusions is a precautionary measure.
He said he was acting on advice from the Department of Health's expert group on this issue.
He said people who have had transfusions may have a slightly increased risk of contracting the disease compared with the rest of the population.
However, he stressed that the increase was probably tiny.
He said the decision to introduce the ban was about "balancing risks".
The Department of Health has also introduced a series of measures since 1996 aimed at making UK blood safer.
These included the removal of white cells from all blood. These cells are believed to be more likely to harbour vCJD.
Many blood products used in the UK are manufactured using donated blood from elsewhere in the world.
Will blood supplies run out?
The National Blood Service collects 2.5m donations each year. It says it needs 9,000 donations of blood each day to treat patients.
About 1.7m people in England and north Wales regularly donate blood. The Department of Health estimates that 50,000 will be affected by the ban.
However, other experts believe the figure could be much higher.
The department has ordered NHS hospitals to try to cut back on the amount of blood it uses in a bid to protect supplies.
Sir Liam Donaldson, the chief medical officer for England, has been asked to draw up a strategy to ensure the NHS uses blood stocks more appropriately.
Mr Reid has also urged those who can donate blood to do so.
The National Blood Service is expected to launch a new advertising campaign urging people to donate blood in the light of these latest developments.