I have no idea what the film is or who the actors were, but someone might remember the scene. I have a feeling it may have been something like Play For Today or a T.V. drama rather than a film. I know my parents watched Dixon of Dock Green and Z Cars - so it could have been one of those episodes. I saw the programme as a child in the 1960s.
The scene involved (I think) a couple visiting their neighbours in their living room. As they got up to see themselves out, they put on leather driving gloves and - when they were behind their neighbours chairs - they strangled them at the same time using lengths of cord or ties or something similar. I think it was a man and a woman visiting a man and a woman. It was so shocking to me at the time because it was a very normal activity with a totally unexpected outcome.
Of course, with time, I may have got this very wrong, but I have often wondered what that programme was and would be so thankful if anyone knew. :-)