Re: Don't talk to the police
You do not have to say anything. However, 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.
Wikipedia says that the "harm" may be thus:
Adverse inferences may be drawn in certain circumstances where before or on being charged, the accused:
fails to mention any fact which he later relies upon and which in the circumstances at the time the accused could reasonably be expected to mention;
fails to give evidence at trial or answer any question;
fails to account on arrest for objects, substances or marks on his person, clothing or footwear, in his possession, or in the place where he is arrested; or
fails to account on arrest for his presence at a place.
Keeping quiet is not always the best policy as they have you coming and going.