Penrose 3.227 

Dr McClelland and Dr Gillon were asked to reconsider this area (stricter vetting of donors in the 1980’s). From their responses, it appears that, with very limited relevant factual data, they attempted to make a conservative estimate.[226] Dr Gillon's explanation tends to underline the lack of numerical underpinning for the estimate:

We knew that the donor selection procedures introduced by November 1984, including as they did a signed declaration by each donor that he or she was not in the defined risk categories, led to the exclusion of a steady number of such donors throughout the period leading up to HCV screening in 1991. I received a written confidential report on every such donor, and therefore had first hand, if somewhat impressionistic knowledge of the apparent effectiveness of the procedures. In order to try to give this a numerical basis, we tried to extrapolate backwards as best we could from the reports on population prevalences published in the early 1990s and subsequently, in order to estimate what proportion of potentially infected donors we were managing to exclude ....

After commenting on HIV among intravenous drug users in Scotland, the discussion continued:

[W]e knew that the initial period of screening for HCV in 1991/2 produced a donor prevalence of 0.09%. Balogun et al (2002) estimated that the populationprevalence in England and Wales peaked in 1986, at just over 1%. By 2005 the HPA (Hepatitis C in the UK. 2011 Report) estimated a prevalence in adults of 0.67%.