The good old fashioned two out of three rule worked well so UK airspace
There has never been any such rule!
Notwithstanding which it was the attempt to get me to sign up to 50 hours of a full PPL course that hacked me off.
If you hold any ICAO licence you only need to meet the requirements for a licence conversion which depend upon your total hours. Probably 2 written exams and a Skill Test plus radio licence.
For ICAO licensed pilots to operate G Reg EASA aircraft see
ORS4-1301
To fly Annex 1 G-Reg aircraft any ICAO licence is valid ANO Art 150