I'd still want to see a blue card or whatever it is.....
playing devil's advocate here - but that is only good for reporting things the person has been caught for. kinda pointless really - the police check means nothing - particularly in situations like the one Niliac mentioned - he was 19, he may have offended previously, but probably didn't have a record. those cards ONLY show whether they passed a check of their record in regard to sexual and physical abuse cases they've been convicted of...

you need to be confident that your carer has your childs best interests at heart, that the child is never left unsupervised with anyone else etc.