I'm not seeing the analogy with the Fifth Amendment. The point about the Fifth Amendment is that you can't be punished for refusing to offer self-incriminating testimony (e.g. by being held in contempt of court). So it's not merely protecting you from whatever prejudices the jury might have about someone who refuses to testify. It's preventing you from being punished for the mere act of refusing to testify (whereas you cannot punish someone in the UK merely for refusing to answer police questions – except in a handful of very specific circumstances).

Indeed, yes, prosecutors have more free rein in the UK to suggest to the jury that someone's silence during question is incriminating. I just wonder if this makes much of a difference in practice. Do you know of any examples of cases in Britain where a conviction would most likely not have been obtained if the prosecutors were not permitted to do this?