as far as i know, the more recent the check was done the more reliable it is, so obviously if a check is 4/5 years old it's not as reliable as a check that was done 2 months ago, guidelines from the agency that we use say that every new member of staff should be checked reguardless of how old or recent their check is.

The problem comes when you have a member of staff who has been with you for several years and you want to renew their check, because as I understand it checks on new members of staff are free, but if you just want to renew a check for an 'old' member of staff you have to pay for it!