I watched this on British tv in the late 1960s/early 1970s - no later than 72..I remember it was black and white but my parents never got a colour TV until 1976!
It was a B movie or a TV movie set in a society similar to 1984 and Big Brother, you were watched for signs of dissent against the government - however this society had a fully fledged rebel organisation with secret codes and hideouts.
One scene a couple of rebels were watching rebel captives being taken to execution, they were mouthing hatred along with the other onlookers while simultaneously passing whispered instructions to one another. I think an armed uprising was being planned.
I think the accents were a weird sort of mid Atlantic so probably it was intended for both the US and the UK
Unfortunately my mother decided she wanted to watch some old romantic drama so I never saw what happened