Confessions constitute an important exception to the hearsay rule. They are attractive to police officers, for obvious reasons, and can impress juries. However, experience also teaches that confessions can prove unreliable and, regrettably, even lead to miscarriages of justice. The source of a confession’s unreliability may lie in the methods used to extract it: if obtained by coercion, which can cover forms of
pressure as varied as torture at one extreme to far more subtle means of inducement presented to the suspect at the other, there is a plain risk that the confession may prove untrue; and this is quite apart from any further consideration that, as a matter of policy, the law cannot simply be seen to have any truck with confessions obtained by especially devious or overreaching methods. Alternatively, a confession’s unreliability may stem from the constitution of the suspect: that person may be unusually suggestible, or may happen to be interviewed while in a vulnerable frame of mind or an impaired state, or may actually be suffering from a mental illness or identifiable personality disorder. In all these cases it has been found advisable to be circumspect about admitting confessional evidence. Unreliability,
then, is far from being the only reason for which improperly obtained confessional evidence is excluded in English law. As Lord Griffiths observed in Lam Chi- Ming v R [1991] 2 AC 212, 220:
. . . [T]he more recent English cases established that the rejection of an improperly
obtained confession is not dependent only upon possible unreliability but also upon the
principle that a man cannot be compelled to incriminate himself and upon the importance
that attaches in a civilized society to proper behaviour by the police towards those in their
custody.