If evidence of wrongdoing is uncovered through improper investigative measures, what protections are there for the subjects of these improper investigations in U.K. law?
Must one still answer for evidence of any wrongdoing no matter how it is obtained or are there any mitigations for this based on investigative impropriety?
There isn't an automatic exclusion rule for all forms of improperly acquired evidence in the UK. I can't find the exact quote but there was a judgement from a senior court that said in terms: "it's not the court's job to discipline the police but to see that justice is done."
However, judges have the discretion to disallow individual pieces of evidence if they think the interests of justice require it. Section 78 (1) of PACE (1984) has:
In any proceedings the court may refuse to allow evidence on which the prosecution proposes to rely to be given if it appears to the court that, having regard to all the circumstances, including the circumstances in which the evidence was obtained, the admission of the evidence would have such an adverse effect on the fairness of the proceedings that the court ought not to admit it.
Senior judges have been reluctant to lay down general guidelines, holding the trial judge best placed to make these decisions (although of course, subject to appeal). The foundational principle is the accused's right to a fair trial, so in principle one could appeal to the ECtHR under Article 6. However it generally takes a similar line to courts in the UK:
It is not the role of the Court to determine, as a matter of principle, whether particular types of evidence - for example, unlawfully obtained evidence - may be admissible or, indeed, whether the applicant was guilty or not. The question which must be answered is whether the proceedings as a whole, including the way in which the evidence was obtained, were fair.
PACE Section 78(2) is:
Nothing in this section shall prejudice any rule of law requiring a court to exclude evidence.
The general principle in 78 (1) does not override specific prohibitions: for instance, intercept evidence is never admissable under the Regulation of Investigatory Powers Act 2000.
In all other common law jurisdictions, including the UK, police who behave inappropriately are subject to employment, administrative and judicial sanction as appropriate for their wrongdoing.
Whether evidence gathered inappropriately is admissible is a matter for the particular judge who must weigh the probity of the evidence against the wrongdoing and decide where the interests of justice are best served. It is not automatically admissible nor is it automatically inadmissible.
