It is a waste of administrative time to carry out an identical check on the same person. If it is established that I am fit to be in a school, this should cover me for any like activity, eg giving children riding lessons, etc.
Let one crb check serve to cover all the employments of one person. At the moment I have to get one check for each school I am invigilating in. Surely one check would establish that I am a fit person. Let the rule for renewal every year still stand.