I've been catching up with my recordings of this early 70s suspense series from Thames and have found them all enjoyable so far and would recommend them to anyone here. And it has a very creepy theme tune.
So far, only one episode, The Death Watcher, has gone into what is definitely horror/supernatural/SF territory. John Neville kidnaps Judy Parfitt to help him prove life after death. It's a strong story that could probably work if remade today with a longer running time.
The final episode in the series, The Party's Over, was shown almost two years after the rest of them and runs just half the length. It may, or may not, have a supernatural element to it but it is so incoherent that it's hard to tell. I wonder if there ever was an unbroadcast 50-minute version that made sense but ended being cut down.