Thanks for the various replies. I discovered my out of subscription Spyware Doctor could deal with it so I renewed and zap ... it's gone. It was particularly malicious in the true sense of the word, pretty much blackmail really and I was stressed because the delay factor was intended to cause the worry of others spotting the invoice for porn - better to pay up than argue about it.

Since Easyjet and Ryanair offer 1p flights to South of France, I've given up buying porn magazines in favour of ogling the real thing.

Cheers, Brian.