Lee Carter reports from Toronto

The committee said people who have eaten British beef since 1980 could carry a form of Creutzfeldt-Jacob's Disease (CJD).

It recommends a blanket ban covering the last 18 years because it says it is almost impossible to predict who will become infected.

And it says there is no easy way to separate those who have eaten beef in that time from those who have not.

Blood products

The committee, the Bayer Advisory Council on Bio-ethics, was set up by the drugs firm Bayer, which supplies the medical world with human blood products.

However, there is no scientific evidence that people can contract CJD via a blood transfusion and there is no test to see if someone is carrying the disease.

Canadian authorities responsible for the nation's blood stores rejected the panel's recommendation.

Transfusion official Graham Sher said: "If we were to stop collecting blood or blood products from people who have travelled to Britain, it would essentially decimate the Canadian blood supply."

Contamination risk

However, the committee, which was composed of doctors and nurses, defended its finding.

It said its goal was to prevent the blood supply from becoming tainted as it did with the HIV virus or the hepatitis C virus.

Dr Burleigh Trevor-Deutsch, the committee's president, said: "Anybody who is engaged in a dangerous activity or risky activity is equally excluded."

CJD is thought to be related to mad cow disease

He said the risky activity in this case was having eaten British beef contaminated by bovine spongiform encephalopathy (BSE) - "mad cow" disease.

Scientists speculate that BSE could be linked to the appearance of a new form of CJD, known as new variant CJD (nvCJD).

The European Union banned worldwide exports of British beef in March 1996 after the government admitted that there was a probable link between BSE and nvCJD.

The UK's National Blood Service said the report was a matter for the Canadian government, but that there was no reason to stop people giving blood in Britain.

Theoretical risk

Sue Cunningham, the organisation's national donor services manager, said there was a theoretical risk that nvCJD could be transmitted by blood but there was no firm evidence to suggest this was actually the case.

However, the service had taken steps to prevent any possibility of infection, she said.

"At the moment the risk is theoretical. There have not been any cases of nvCJD so far linked with blood," she said.

"But that does not mean you can say it could not happen. That is why we are co-operating with the government on these precautionary measures."

The measures include removing all the white cells from blood before it is used (in a process called leukodepletion) and importing blood plasma from the US.