I think Tesco, Sainsbury's etc are just resellers of banking services. Actual banking licenses are the thing there have been none of for 100 years iirc, I don't think GP comment just pulled that assertion out of thin air.
So that claim might have been true few years ago before fintech boom started. Lots of new digital banks already got or are in process of getting banking license.
Banking industry in U.K. is getting shaken up currently, lots of fintech challengers.