Those towards the end of the alphabet went to Coutts, the rest to Lloyds.
Cox’s & Kings. Taken over by Lloyds in 1923. It was always nice to visit the branch in Pall Mall and deal with someone with numerous aircraft prints on the wall of their office who understood how RAF officers know and pay were linked.
Still with them, but now a PO Box somewhere in Chelmsford…..
https://www.jstor.org/stable/44229113