There is no fundamental right to silence in UK law.
"... it may harm your defence if you fail to mention, when questioned, something you later rely on in court. Anything you say ..."
Anglo Saxon law traditionally allowed for the payment of compensation to a victim's family in lieu of imprisonment or physical retribution. Locking people up for prolonged periods in jail is a comparitively modern trend, fines or physical punishments were much more likely to be used as a deterrent to wrongdoing.