CEP
Between 1956-63, a total of 133 BEP/CEP units was introduced, basically for operation on the Kent Coast electrification scheme.
The CEP units were the first main line sets built to BR standard coach design, based on the Mk. 1 fleet of the period. Construction of CEP four coach units was carried out at Eastleigh and, by mid-1956, the first of four pre-production sets emerged as No. 7101. The unit had end corridor connections with a a full gangway. Technical equipment was similar to that used on BR-designed EPB stock. The formation of the four car units was: Motor Brake Second Open (MBSO), Trailer Composite Corridor (TCK), Trailer Second Corridor (TSK) and MBSO. MBSO vehicles contained the driver's compartment, with a guard's and luggage van behind, followed by passenger accommodation in an open layout. The two trailer vehicles were of similar construction, one housing three second and four first class compartments, and the other eight second class compartments, access to both vehicles being by a side corridor. Traction equipment for the fleet was two English Electric 250hp traction motors, mounted on the outer ends of each MBSO vehicle. The four prototype units operated on the Central Section and proved to be highly successful. A production fleet, given Nos. 7105-53, was ordered during 1957/8, and these were destined for phase 1 of the Kent Coast electrification scheme. They closely followed the prototype sets, but incorporated some modified technical equipment. A further fleet of units was ordered in 1960 for the second phase of the Kent Coast electrification scheme, and numbered 7154-7204. During 1962, a further seven units, Nos. 7205-7211, were ordered for the South Western Division, but these soon joined their brothers on the South Eastern Division.

BEP
To work with the CEP fleet, a batch of buffet units, classified BEP, was ordered. Two BEP units, Nos. 7001-2 worked with the four prototype CEP units. Construction was carried out alongside the CEP build at Eastleigh, and was identical, except for a TRB buffet vehicle, with 21unclassified seats, replacing a TSK. Power for the buffet car was provided by its own motor generator mounted underneath. When the CEP production fleet was authorised, buffet sets were also ordered. Nos. 7003-7012 were for use with Nos. 7105-53, and Nos. 7013-22 for operation with Nos. 7154-7204.
The allocation of units remained constant for many years, with prototype sets Nos. 7001-2 and 7101-4 being used from Brighton, and the production sets from Ramsgate. When delivered, units were painted in BR green livery which subsequently changed to rail blue, and later to blue/grey.

With little possibility of new main line stock, a decision was taken to carry out a major refurbishing programme on the CEP/BEP fleet. Prior to large investment being made, set No. 7153 was experimentally refurbished at BREL Eastleigh. The work included alteration to the unit formation; the brake compartment was removed from the driving cars making these DMS (Driving Motor Second). The former trailer composite was rebuilt into a trailer brake composite, while the trailer second compartment was altered to an open carriage. After evaluation of No. 7153, a full refurbishing programme was authorised, and BREL Swindon was awarded the contract. Transformation at Swindon commenced in 1979, with the final unit returning to the Southern Region in 1984. Quite early in the refurbishment programme it was decided that all buffet sets would not be required, and a number of BEP units were rebuilt to CEP standards, gaining a newly-converted locomotive-hauled TSO in place of the buffet car. It was decided to refurbish seven BEP units for use on the Portsmouth line, and these followed the CEP styling, with buffet cars being completely rebuilt providing a fast food facility.
Refurbished units were given the TOPS number system, CEP units emerging in the 411xxx fleet and BEP units in the 412xxx series.
After refurbishment the 411s were on the South Eastern division and the 412s on South western. However after privatisation a number of 411s were transferred to South West Trains operation.
A number of three car 411 sets have now been formed by removal of the TS vehicles.