Thanks. I have just reported such details as I can via the Action Fraud website, although based on the facts the web program does not consider me to have been the victim of any fraud. I have a reference number which I could quote to the DCA, but no promise that the matter will be investigated by the police.
I am not sure whether to bring up the previous correspondence when replying to these latest letters, as I did not keep any letters (it was, after all, 8 years ago and I thought they had given up pestering me). Most of the correspondence at the time was by telephone unfortunately, although I did get a solicitor to write to them on my behalf. Can't get hold of him for copies of any correspondence kept.
Part of me thinks that these muppets will only sit up and listen if I take a more hardline approach, i.e. the threat of complaints etc.