Armchair Cinema or possibly ITV Playhouse: Suspect

Perhaps I had better start by explaining my title. If you want to see this on YouTube the thing to search for is Armchair Cinema. I think it may be on one of the Network box sets of that name but I'm not certain. If you want to read about this show on IMDB, it is under the title of ITV Playhouse here.
Wonderful TV this, proper quality. And you all know how difficult it is to get unalloyed praise from me. Settings, visuals, plot, characterisation, acting, all superb.
It may, however, be rather wrongly named, because this is much more of a psychological thriller than a Whodunnit. It gradually and effectively builds up the tension, mostly revolving around Mrs Segal, some of whose actions are rather bizarre and she backs herself effectively into a corner. There is also a feeling of claustrophobia about this because so much of it revolves around a single house and a single village.
The house is absolutely gorgeous, but don't please run away with the idea that we are talking about one of our ancient landed families: being in trade, the Segals are distinctly nouveau.
What strikes me is how old fashioned it is, but then it is fifty years old. I doubt any village functions that insularly now, but then since the country terrifies me I would always have hated it. I love the way everyone lights a fag at the end of a meal. And Mrs Segal's car is a mark 3 Ford Cortina, and my dad had one of those!
Superb television. And superb acting by some Big Names who show their quality by not overpowering their roles.