Few would disagree with the verdict of Lord Winston that the use of contaminated blood in transfusions and blood products was "the worst treatment disaster in the history of the NHS". Thousands of people in the UK, including an estimated 4000 in Scotland, were given contaminated blood in the 1970s and 1980s. As a result, many, including more than 2000 haemophiliacs in the UK, have since died from either hepatitis C or HIV, and there is a fear that others remain undiagnosed. Campaigners for a public inquiry into what went wrong have argued for many years that if this scale of carnage had occurred in an accident, there would have been a full-scale public inquiry long ago.

That did not happen because this was a systemic failure which took place more slowly in a series of personal tragedies to individuals. Among them were Eileen O'Hara, who contracted hepatitis C after two heart operations and died aged 72, and David Black, a haemophiliac who was also infected with the virus from contaminated blood and died aged 66. There was no dispute that each had been infected as a result of their medical treatment, but despite the obvious public interest, the Lord Advocate refused to hold fatal accident inquiries into their deaths. Immediately after that decision in 2006, the then Health Minister ruled out a judicial inquiry into infection with hepatitis C through NHS treatment in Scotland, on the grounds that it would yield little new knowledge.

Their families, and the thousands of others affected, were left with unanswered questions. In particular, concerns have not been publicly examined as to why heat treatment for blood products in Scotland was started 18 months later than in England; why there was a delay in screening blood donations; and what steps have been taken to trace people who may have been infected. Lord Mackay of Drumadoon has struck a valuable blow for all of us in ruling that the refusal of the Lord Advocate to hold fatal accident inquiries and of Scottish ministers to hold a public inquiry into the deaths of Mrs O'Hara and Mr Black breached the European Convention on Human Rights.

It is an article of the convention that everyone's right to life shall be protected by law, and that includes the right of someone who dies following treatment in hospital to a practical and effective investigation of the facts relating to their death and determination of any civil liability. In theory, the O'Hara and Black families could have raised civil actions, but that would not have resulted in the full investigation they want. Both have made it clear they have no criticism of the medical staff who cared for their relatives, but only of the system surrounding the use of blood donations.

Although an inquiry is under way in England under Lord Archer, the former Solicitor General, into the circumstances surrounding the supply of contaminated blood and its continuing consequences, it is funded by private donations and its findings will not be legally binding. The SNP has made a commitment to hold a judicial inquiry and this must now go ahead, so that all the lessons can be learned, and families who have fought for so long finally get some answers.