As far as I know, the major change came in the 90s in the form of "it may harm your defence if you do not mention when questioned something which you later rely on in court". In other words, the court can draw conclusions about something you initially refused to comment on, but then later answered as part of your defence.
Actually it was even earlier than that; adverse inferences could be drawn from silence after the passing of the Police and Criminal Evidence Act 1984.
What a fitting year!
You can still remain silent but a jury is allowed to infer possible guilt from your refusal to answer questions.