So, if you are arrested for beating up X, and you invoke your right to silence, THEN at trial you put forward a defence of "I wasn't there!" without any substantive evidence to back it up, the prosecutor can say "well, look, if there was an alibi, why didn't you tell the police about it?" The judge is supposed to then instruct the jury that they can draw an inference as to your honesty on the grounds you didn't bring it up during police interview.
The legislation that brings that into force are ss34-39 of the Criminal Justice and Public Order Act 1994.
https://www.legislation.gov.uk/ukpga/1994/33/part/III/crossh...
absolute nonsense
the statute with the meaning that you are trying to whitewash your argument applies only to application for dismissal of the indictment based on a claim it's reasonable for you to have provided earlier thereby preventing the proceedings progressing to court
this is my understanding of the UK system too (note: I am an american). it's quite different in the US because, among other things, the jury is explicitly instructed not infer anything from the defendant's use of their 5th amendment protection against self-incrimination. even if you have a perfect explanation for what happened, it's often best to just be quiet and let the prosecution fall apart.