The two 4DD electric multiple units were the only double-deck trains to run on the main line railway network in Britain. They were somewhat unsuccessful because of the way that the upper level seats had to be squeezed in between the lower level seats to ensure that the overall height of the unit would be within the clearances necessary to pass through tunnels and under bridges. To obtain the extra seating capacity that was being sought, it was decided to lengthen trains from 8 cars to 10 instead.

Formations

 Unit Numbers DMBT TT TT DMBT 4001 (later 4901) 13001 + 13501 + 13502 + 13002 4002 (later 4902) 13003 + 13503 + 13504 + 13004 

Preservation

Driving Motor cars 13003 and 13004 survive in preservation, the former at a private location in Ashford, Kent, and the latter at the Northampton Ironstone Railway Trust. One trailer car was also saved after withdrawal, but has since been scrapped.