CRB checking in its preent format is a disincentive to volunteers. It particularly impacts on the retired generation who may well have spent most of their lives volunteering and view it as an insult.
Currently it is neccessary to have a CRB check for each organisation you volunteer for. It is a disincentive. Make one CRB check cover all organisations even if it needs to be more comrehensive initially. Eliminate the need for a CRB check where the volunteer is only going to volunteer once for a few hours. Consider whether in some cases references could take the place of checks.