This must be done by employers or agencies. I am qualified teacher and as such have a current CRB certificate requested by the organisations that employ me. I do understand that in some cases these are not portable.
Therefore, if I am undertaking work which requires a standard or enhanced DBS (CRB) disclosures, for example, photographing children or vulnerable adults on location at schools, play groups, activity centres, churches or other religious buildings etc, if portability is an issue then it is the responsibility of the requesting organisation (of the work) to seek a check on me. I am more than happy to submit to any required and valid DBS (CRB) requests.
It should be emphasised that as a professional photographer, I am not employed by the school/organisation, and therefore have NO responsibility for the children. The teachers/carers (who must be DBS/CRB checked) are employed to have that responsibility and therefore should ensure I am chaperoned at all times in the presence of children/vulnerable adults