If you are arrested in the UK, you'll hear that your rights include a rider inserted by the 1994 Criminal Justice and Public Order Act, after "you do not have to say anything":
But, it may harm your defence if you do not mention when questioned something which you later rely on in court.
In common with, I think, many British laymen, I have never understood the justification for this change, and have only ever seen it as vaguely threatening and a non-specific erosion of civil liberties. At the same time, I'm not really sure what specific sort of abuse I have to fear from it.
Can anyone provide me with understandable, concrete examples of
Why (if at all) I should be thankful that this clause exists? i.e., What kind of criminal act might a criminal get away with if this rider weren't there?
What I have to fear? i.e., (a) What's the worst that might happen to a distrusting but innocent person who is wrongfully arrested and decides to say nothing? (b) How might the negative consequences have been avoided by saying something? (c) What additional risks are entailed in opening one's mouth in this situation, and how can they be minimized?
EDIT: having read Nate's interpretation and Dawn's comments, I can re-frame the question more specifically. Either A: there was a simultaneous change in the way a suspect's silence could be used or interpreted in an English/Welsh court (away from the US model in which prosecutors cannot even draw attention to it), and the change in wording reflects this erosion of civil liberties; or B: both before and after the Criminal Justice Act, silence could always harm your defense, and the change in wording is an entirely benevolent attempt to warn people of this fact. Can anyone tell me which is the case?