 Under British Railways ownership, the class was reclassified from 4MT to 4P5FB in 1953; the "B" denoting the brake power rating when used on unfitted (non-vacuum braked) goods trains.The locomotives at first retained their Southern Railway livery, but with "British Railways" painted on the tender in Bulleid block lettering.Eight locomotives had light repairs prior to 1950 and were given an "S" prefix to the Southern number ("e.g."