It had no underframe, but the whole body was formed into a welded stress-bearing box girder made of 1⁄8 inch (3.2 mm) solid drawn steel tube.

The corrugated steel floor was filled with sprayed asbestos and covered with asbestos-filled flame-proofed hardboard and rubber sheet.

[1] The units soon became non-standard and two were sold back to the manufacturer who exported them to Trinidad and Tobago.

Another unit was converted into departmental service, and survived in BR ownership until the early 1980s.

One two-car set (50416+56171) was extensively overhauled in 1967 at Doncaster, revamping the interiors and adding kitchen facilities to 50416.