That's not a police caution , as in 'accepting a police caution'. It's just the form of words which the law requires an officer to say when he wants to question someone or speak to them when he suspects an offence has been committed and that they've committed it.It tells them of the right to stay silent but adds that if they don't say something which they later rely on in their defence their failure to say it may harm their defence (e.g. because the suggestion may be that the defence is a late invention)
A police caution is a formal procedure at a police station whereby a person is told that they can accept a police caution, which would amount to an admission of the offence., .Accepting the caution means that they won't be convicted of the offence in court.It's a way of disposing of cases without going to the expense and trouble of securing a conviction. That's not your case.