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The Codes of Practice associated with Police and criminal evidence act (1984) set out a number of rather complex rules about when and how a police officer should caution a suspect before questioning him. In essence, however, it comes down to this: a suspect should be cautioned before asking any question that could reasonably be expected to be offered in evidence. A suspect doesn't have to be cautioned before asking his name or address. If a suspect makes statements before a caution, he should generally be given the opportunity to retract them after caution.

Because the Criminal justice and public order act (1994) allows a court to make inferences based on a suspect's refusal to answer questions, the Codes of Practice require that the caution warn suspects of this. The recommended fomr of caution is:

You do not have to say anything, but it may harm your defence if you do not mention anything when questioned that you later rely on in court. Anything you do say may be given in evidence.