"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. Anything you do say may be given in evidence."
This is, as I understand it, very different to the US right against self-incrimination where the courts are specifically not allowed to infer guilt from silence. (Although I suspect many juries may be influenced negatively by someone remaining silent, despite direction.)
Except (as I hear it) that's not even true in the US. Apparently, it's not enough to stay silent - you actually have to say that you are exercising the right to be silent, otherwise they are allowed to infer guilt from silence.
In a very similar way, if I were ever detained in this manner in the UK, I'd be very likely to say "I am not refusing right now to answer your questions. However, since I cannot trust you to tell me the truth about my rights and responsibilities, and because of the power imbalance, I will wait until I have independent legal advice before participating any further in this interview".
Even the right to a lawyer has been denied because a judge chose to endorse a police interpretation of "I want a lawyer dawg" as a nonsense request for a dog-attourney.
(The 'Police Caution', see: https://www.gov.uk/arrested-your-rights )
This is, as I understand it, very different to the US right against self-incrimination where the courts are specifically not allowed to infer guilt from silence. (Although I suspect many juries may be influenced negatively by someone remaining silent, despite direction.)