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The government’s expert advisers assume that as many as 15,000 people in this country are infected with the prion infection agents that cause the lethal brain disease, variant Creutzfeldt-Jakob (vCJD), the human form of BSE or “mad cow disease”. The experts don’t know if this is the right figure. It could be a lot higher but ministers are refusing to fund trials of a new test to find out.

So far just 200 of our fellow citizens have developed the disease. But the prions that cause the disease can lie dormant for decades and people who are infected pose a risk to others if they are blood or organ donors, or if surgical instruments used on them are then reused on other patients.

The Medical Research Council Prion Unit at the UCL Institute of Neurology, led by Professor John Collinge, was set up at my behest to come up with ways to treat vCJD and, better still, prevent it. They were also asked to devise a test to identify vCJD in the general population. They recently announced a new blood test that does just that. This is a great breakthrough. It should enable our doctors and scientists, for the first time, to assess accurately the incidence of vCJD infection so policy decisions on how best to protect patients can be based on evidence, not guesswork.

As health secretary, the day I became aware in 1998 that it might be possible to transmit vCJD by blood and blood products, I got the experts together. Their advice was that infection through blood and blood products was likely but not certain and that the infection, if any, would probably be carried in the white blood cells. “What should we do?” I asked. The answer for the blood supply was leucodepletion (removing the white cells) at a cost of £100m. When I told Tony Blair that I’d authorised spending this £100m but hoped it would prove to be a waste of money, his response was “fuck me”. The blood for a transfusion usually comes from just a few donors but blood products come from many more donors, so the chances of infection were much greater. I had to agree that we should end UK sourcing of blood products – easier said than done.