As I understand it this issue is:
SC checks the details of the person and assumes that the person’s identity has been confirmed.
BPSS is supposed to confirm the identity before the SC checks are carried out.
The SC is worthless if the person on which it has been carried out is not actually the person we’ve got.
There is apparently now some issue that the method we have been using to confirm identity does not satisfy the requirements for SC.
So, whilst unlikely, it may theoretically be possible that Mr John Smith with a clear SC check is actually convicted fraudster Mr Joe Bloggs who presented himself in the beginning with a stolen identity and fake ID.
…and obviously the MOD processes don’t deal in probabilities they just say “BPSS is the required standard - you haven’t been doing that in the past so now everyone needs to complete it retrospectively”.