I remember a few years ago a police air suport unit got fooled into beliving a chap was a CPL(H) in fact the pilot was in fact a PPL(H).
The PAS unit manager and chief pilot who were good guys interviewed him and he passed the flight assesment te in the EC135, and offered a job, only to discover that he had forged the CPL(H). I will not comment on the manufature of forged licences here, but it was quite impressive someone not military trained or with commercial experience could pass the flight test.
It got in to local media, but then the police and the CPS quietly dropped the case, as I think it was highly embaressing for the police.
But isn't it odd I can check a doctor, radiographer, social worker, solicitor, online, but not a pilot. Likewise a care hire company can check your licence online (with your consent) from anywhere in the world.
When I examined PPLs who hadn't met me before, I would often ask at the end of the flight test why as PIC U/S why they hadn't asked to check my licence, medical and examiner authorisation, as it is a check list item. I should also say when I have hired aircraft from flying schools I have rarely been asked for my licence, but in part because I was a familiar face at airfields.
I think there is alot of complacency about licences and the CAA could make it easier for instructors to check licences, not least post 911 to give the instructor peace of mind.