Infact the 737-400’s were delivered in Landor blue colours before any 737-300’s were in the fleet. 737-300s coming from various sources.

Incorrect. The first 737-400 was G-DOCA registered in the UK in 1991. First 737-300 with British Airways was OY-MMP, subsequently G-CMMP, initially operated on the Danish register but registered in the UK in 1988 on lease from Maersk Air to British Airways (this one was the one I was wondering was in red-tail, but evidence suggests it was in Landor).

Andy