I seem to have fixed the issue but I'm not sure I've done the right thing.
Follownig some fairly commn advice from the results of a Google search, I've disabled the Anti-circumvention filters in Adblock and it all seems to be working fine.
Perhaps there's someone here that knows more than I do* on the subject can advise?
* Clearly most of you know more than me, but you know what I mean!