Thanks BEagle. I'll pass on the pointer to the CAA site.
The sloppy terminolgy was mine - he was a qualified (civvy) Flight Instructor.
I'll pass on the warning that he shouldn't expect too warm a welcome from 'the many eager young FI(R)s'. He genuinely enjoys instructing, kept it up even though flying airlines, and let his licence lapse only because domestic commitment prevented him from continuing for a few years.