I browse & post here but rarely, Sir. The Rules eg forbid my posting of the URLs as you request, and once modified, further delayed my reply.
For this sort of personnel case, you'd find the RAF Commands Forum a congenial place, with real expertise.
Air Force Lists (from the Internet Archive)
Readily searchable
AFL July 1945 finds Brett listed as S/Ldr A&SD, wef 1 Jan 1944.
1919 AFLs : He does not appear post-war as far as I can see: the only close match in all issues being
Brett R de R MC (Lt, Aeroplane and Seaplane Offr Br, 1 Apr 18) (in May 1918 AFL)
The London Gazette
Search on Brett 79293 finds 5 RAF entries from 1940 to 1954 (relinquish of commission)
Search on "Ronald Dallas Brett" (inl quotes)
yields 2 pages of entries from 1927 to 1962 as solicitor, and for OBE.
including one 2 Nov 45 indicating shortly prior return to private practice.