There have been many studies of the prevalence and vulnerability of persons with learning disability within the criminal justice system. During Victorian times and the ‘eugenics era’ early in the twentieth century, many held the unscientific view that all ‘feeble-minded’ people were at least potentially offenders. More recent studies in the UK have shown, however, that persons with learning disabilities are not over-represented—fewer than one per cent of convicted persons are identified as having a learning disability. However, it can certainly be argued that such people may be in a greater danger of coming into contact with the criminal system because they may be poor and socially disadvantaged, less likely to evade arrest, and less likely to obtain a fair trial.
As in Ireland, persons arrested and detained in Britain are cautioned, advised of their rights and given a ‘notice to detained persons’—a rather complicated printed form. Isabel Clare’s study (19??) showed that fewer than 8 per cent of detainees understood the caution or the notice, or that they could have a solicitor. During police interviews, persons with learning disability are known to have a tendency to ‘interrogative suggestibility’; they come to accept messages communicated by authority figures (i.e. the police) and to acquiesce with ‘yes’ answers to questions put to them.
The UK Police and Criminal Evidence Act—Code of Practice (1995) calls for the provision of an appropriate adult to advise and observe in cases where persons with intellectual or mental health difficulties are in police custody. One study showed that out of 20,000 cases, only 38 adult suspects were so represented (the statistical prevalence would indicate a number of about 1400). Reasons given for the failure to provide ‘appropriate adults’ included difficulty in identifying learning disability needs, delays in finding and/or arrival of the designated appropriate adult, and attitude/competence of the appropriate adult. Dr Murphy noted that Cambridge Custody Officers had devised a useful information sheet suggesting the sort of questions to ask a person in custody to identify special needs/learning disability.