There is now, and I think there has always been, a register of amateur radio operators in the UK. I know because I am an amateur radio operator.That register would give you his name, location and callsign. It is likely his callsign at that time might have commenced G2+2 letters or G3+2 letters or G5+ 2 letters
The Radio Society of Great Britain may be able to help at
https://rsgb.orgI have a licence to transmit and a listing in the callsign handbook that I have mentioned would have been conditional on him having a similar licence. If not, he may have registered as a shortwave listener. I think at that time operators would have been regulated by the Post Office so there might be something in Post Office records about him.
The only requirement for him to operate as a Y station would have been competence in reading morse which doesn't mean he was necessarily a registered radio ham as such. He could have been a commercial telegraphist...a Marconi man or similar.
Looking back through the thread it seems likely that he was a commercial telegraphist with Cable & Wireless or even a marine radio operator.