Introduced from 1967 the 4-VEP fleet were one of the main modernisation fleets on the former Southern Region and were soon to be found working on all three section, South Western, Central and South Eastern. The sets offered good quality travel in mainly open saloons (the first class being in compartments), the high-density layout of 3+2 seating and a door by each seating bay found considerable favour with passengers, especially in peak periods. The sets with a central power car performed well and eventually over a seven year period 194 sets were built. Originally units were finished in rail blue, but as the grey and blue scheme was adopted sets emerged in this colour. Following the formation of Network South East in the late 1980s, the red, white, grey and red livery of this operating arm of the then BRB was applied.
As part of a major facelift programme on the late 1980s and early 1990s, extra second (standard) class seats were installed, by converting half of the original rather large luggage van to seating accommodation.
Upon privatisation the VEP fleet, by now classified as 423/4 for refurbished sets were allocated to Connex and South West Trains and both operators soon applied their house colours. From 2001, after the Connex South central franchise was taken over by GoVia the green and white of the New Southern Railways started to appear.
A major modification took plate in 1999 when a batch of 19 sets were modified to 4VOP, by having the original first class compartments removed and open side access standard class seating fitted, this modification rendered the sets as second class only.
For a short period from 1978, 12 VEP units were modified for use on the Victoria-Gatwick Airport service, in the days before the dedicated Gatwick Express service was operated. The modified sets had special luggage stacks inserted in place of some seating bays. Modified units were classified as 4VEG and took the numerical classification 427.
The VAB unit was formed in 1968 to assist with stock for the Bournemouth electrification and was formed of vehicles from VEP sets 7739/41/42, plus a converted loco hauled buffet 1759 which was ep brake fitted and through wired. The set was formed of one three and one 5 car set, each numbered 8001 which always ran together. The set was based at Bournemouth and worked on the Bournemouth-Waterloo route, it was disbanded in 1974 when extra REP sets were introduced.