The SR followed LSWR practice and arranged the corridors so they alternated down the set, but stopped short of having 'handed' Brakes. The 'Ironclads' were the last SR stock constructed with 'handed' brakes, for use in sets with an odd number of vehicles. With an even number of coaches in a set, the corridors will alternate OK, but with an odd number then there will be two neighbouring vehicles which will have their corridors on the same side. The usual arrangement for a 3-set was to have the first-class in the CK to be arranged next to the lower-numbered BTK (corridors on opposite sides) and the other BTK would have its corridor on the same side as the CK. With 5-sets and higher, the situation quickly got messy and sometimes two of the inner vehicles were same-handed rather than the higher-numbered BTK and its neighbour. ...And once they started to include open vehicles...
In pictures from the late-30s onwards, show that some cases the inner vehicles of high-window sets were arranged so that the corridors were on the same side and therefore with one of the brake vehicles, the other one, of course will have the corridor on the opposite side to the rest of the set. Whether this spread to the low-window sets cannot be confirmed, as the corridor windows are the same height as the compartment windows on the other side (most pictures concentrate on the train with the loco in prime position, and the coaching stock is very much in the background and it is very difficult to distinguish a corridor window from the compartment windows at a very shallow angle of view).
When introduced, the Bulleids followed basically the same principle but as the BTKs were semi-open there wasn't the same problem with alternating corridors with the brake vehicles.