When "I have been in this industry longer than anyone on that site" is a cornerstone of your defence, you've already lost. Also, I know the UK has really strict laws, but I doubt he'd be able to sue for "liable".
He doesn't know, and can't know, everyone commenting to HN. At best hes fabricating. I was going to top post that but checked first to see if anyone had surfaced that line.
The auditor is an idiot and feels cornered.
Also: "I'm going to assume you do not have PCI installed on your servers".
PCI is an auditing standard. Not something "you have installed on your servers".
And I guess I'm getting too far ahead of myself, because the OP comments on this in his serverfault posting.
Classic! "PCI SSC have responded and are investigating him and the company. "
This is true but the distinction is pretty minimal. Scots judges have traditionally followed the English lead seeing no sense in having different interpretations North and South of the border for the same story in potentially the same publication.
About the only real difference when it comes to defence is that up here you can defend something based on it being made in the heat of an argument, and that the person claiming defamation has to be able to show harm (though not necessarily financial).
Having been involved on the periphery of a major criminal case which started off as a defamation case (there being no libel in Scotland) I can assure you that that is not the case. Scottish Defamation and English Libel are quite different laws. A number of people have made good money from arbitraging the difference.
I know there are a lot of differences (I'm English and live in Scotland), just my understanding of libel / defamation is that broadly the nature of rulings was similar - essentially that Scotland's system while slightly different wasn't that much better than the English system.