Ted. Thanks for the explanation of the vehicle types mainly used by the RAF, explicit as always.
As for the reason Middlesex registrations were used pre-war in the 1930s was more to do with the location of the county I think than for any other reason. The county covered a large area of the south west and west of what most of us think of as London and when the Greater London Council was formed in 1965 virtually all of Middlesex became part of the new council. The administrative headquarters of Middlesex County Council in the 1930s was at Middlesex Guildhall in Parliament Square, now the home of the Supreme Court, so it was handily placed for government Ministries to pop along and register new vehicles.
And yes I would welcome seeing more of the auction catalogues if Wally can obligue.
Dusty