The Class 122s were effectively a Class 116 DMBS (which were the High Density sets currently in production at Derby) with a cab at both ends.

Construction

Bodies were an all-welded construction, with top hat section vertical pillars and z-section rails. Limpet blue asbestos supplied by J.W. Roberts & Co Ltd was sprayed to the inside of the 16g. steel bodyside and roof panels. Beclawat full-drop windows were fitted to the cast aluminium doors made by Lightalloys Ltd. The saloon windows did not have ventilators, air extraction was through the roof by standard BR type roof vents. The ceiling panels were 1/8 in. thick Laconite. Floor panels were a composite construction of 1/16 in. aluminium, 1/4 in. asbestos and 3/4 in. plywood. These panels were secured by Cyc-Arc studs and recessed barrel nuts. The guards van floor was a bitumastic compound laid on a dovetail section floor sheet, with aluminium chequer dumping plates inside the doors.

The underframe was a welded section of double channel longitudinals and crossmembers, with rolled channel section solebars. Additional longitudinal channel members with gusset attachments provided reinforcement between the bolster positions. Rolled steel sections were supplied by the Ayrshire Dockyard Co. Ltd. Standard type drawgear and Oleo-Pneumatic light steel buffers were used. Some later received oval buffers. Bogies were the conventional swing link bolster DMU bogie with spring side control and side friction blocks. The English Steel Corporation Ltd and George Turton, Platts & Co Ltd supplied the springs, and Taylor Bros & Co Ltd supplied the wheels and axles. The axleboxes were the roller bearing type from British Timken Ltd. Smith-Stone speedometer and mileage recording equipment was fitted. The standard Gresham & Craven quick release vacuum brake equipment was fitted, with 21 in. vacuum cylinders. All brake rigging was in aluminium alloy. Two Clayton Dewandre Co. Ltd. exhausters, belt driven from the gearbox input shaft, emptied the 15 cu.ft. of the vacuum reservoir. An emergency brake handle was fitted in the guards van, and there were hand operated parking brakes in each cab.

Power equipment was the standard set up supplied by British United Traction, with the "A" type engine being chosen. Graviner automatic fire protection equipment was fitted, as was ATC. There were two 98 gallon fuel tanks, as well as a 35 gallon tank to supply the two S. Smith & Sons (England) Ltd combustion heaters where wree mounted longitudinally on each side of the frame between engine and bogie. Batteries were British Railways lead acid A2 type, of 440 A-hr capacity and were charged through a germanium rectifier by a belt driven C.A.V. alternator.

Originally the two exhaust pipes joined together above the destination indicator forming a small box. This was altered in the mid '60s to two separate pipes.

Interior

The cabs had flat top drivers desks. The cab roof and ceilings were fibreglass. Trico-Folberth screen wipers were fitted, and a hand-pump operated water spray unit. Access to the saloon/van was via a sliding door. On the end with the saloon behind the cab, folding blinds were fitted to the bulkhead windows.. At the outer cab doors a tubular commode handle doubled as drain pipes for the roof gutters.

The saloon panels were Formica faced glossy bleached mahogany, with end partitions in Formica faced straight grained walnut. The non-smoking section (20 seats, in the saloon next to the van) was divided of by a Formica faced blockboard partition, with full width glazing above seat level. The fawn linoleum was supplied by James Williamson & Son Ltd. Ceiling panels were an off-white eggshell semi-matt finish. Tubular anodised aluminium luggage racks were fitted above each window and on the compartment division. Ash trays were attached to the door side pillars where appropriate. Light fittings were supplied by J. Stone & Co (Deptford) Ltd.

Seats, in a 2+3 arrangement, were formed of base springs with foam rubber pads and squabs, covered in a "triangle" style patterned moquette, and fitted to Lace Web tubular seat frames. The facings were in blackberry Lionide with fawn piping. The guards van was painted fawn, and contained the usual first aid, fire fighting and emergency equipment.

Later Leyland 680 engines were fitted. The two-character headcode panels were plated over, and the exhaust pipes no longer joined at the top.