"A question that will legitimately arise is as to the relationship between the two types of invasions of privacy (invasion by prohibition and invasion by enforcement mechanism) and the strength of their respective justifications. With arguments about evidence-gathering techniques, the question is to do with process-values, and the usual approach is to say that the more serious the invasion of the privacy, autonomy or dignity of the defendant, the higher the degree of formal scrutiny which is required before it can be invaded. There are some invasions which be undertaken by anyone, some only by police officers, some which can be authorised only by senior police officers, and some invasions which require orders from magistrates, or by more senior judges. There are some invasions that cannot be made under compulsion, but from the defendant's refusal to be invaded can be drawn adverse inferences. Whether or not the additional constraints provide substantial checks or easily surmounted formal obstacles is not here in point: what is of concern is the value expressed by having such a body of rules."