If I had to say anywhere, I'd guess that Nigel came from somewhere in the south of England. However, he doesn't have any of the distinctive traits I'd associate with any particular part of the South. (He doesn't have the burr or rolling 'r's found in parts of the South West, and he certainly isn't a Cockney.)
Nigel's pronunciation is quite refined, so he could be from just about anywhere, depending on the kind of schooling / vocal training he had. On the basis of the accent, I would guess that Nigel either comes from quite a privileged background or that he wants to give that impression.
If it helps, I had a quick look on IMDB, and found out that the actor who played him was from London, so you could go with that.
Actually, now that I think about it, wasn't there some mention in the series of Nigel having been a British secret agent who went bad?
If so, given his age, he could well have been recruited into one of the intelligence services from Oxford or Cambridge universities. My impression is that, for a long time, these were prime recruiting grounds for career civil servants. (Or maybe I've just watched far too much Yes, Minister over the years!)
The backstory also suggests to me that he could be from quite a privileged background, probably having been educated at private (what we call 'public') school / boarding school.
However, bright students from other backgrounds do / did also go to Oxford and Cambridge, so Nigel could be a working-class grammar school boy done good but then gone bad. (Actually, I rather like that idea.)
Maybe I should have written a much shorter post and said, 'I dunno.'
Hope that helps.
Krissie
