CEPs were new for the Kent Coast electrification. Did they work to Havant in 1963 or only later? The Southern Electric Group website says from 1964 which was after Hayling Island closed.
Ceps
predated Kent coast.
Protoype Cep and Bep were simply BR SR Mk1 express EMU versions of SR Cor and Buf, and were devised as standard units for all future BR SR electrifications. That they only ended up as a squadron fleet on Kent coast and no more built is technical drift (away from two end motor coaches to single central motor) and operational drift (away from SR traditional small vans at each end to single middle larger van) => Cig/Big.
It is true the squadron fleet was built for and /mostly/ intended for Kent coast, but they were never limited to Kent coast, neither is it true they were all new for Kent coast.
The first and last units were for, and entered traffic on, CD and SWD respectively.
7001/2 7101-4 entered service on the CD in 1956 which was way before any Kent coast third rail was laid never mind energised.
Some of the last built Cep batches were ordered for SWD - and actually delivered there - they worked Alton services very briefly when new - but quickly sent east.
Cep/Bep formations were a long term part of Victoria Mid Sussex Littlehampton / Portsmouth services taking the traditional LBSCR legacy route; I am not getting into a debate on who says what but refer to
John Atkinson's works
QUOTE
A further batch of units 7205 - 7211 were built in 1963, entering service on the SED and displacing a number of earlier ‘phase 1’ units to the Central Division for the Mid‑Sussex line.
UNQUOTE
Considering that Cep construction lasted until 1963 and 1963 saw P1 units to the CD, and Brighton retained a Cep/Bep allocation well into 1980s, then 1980s concentrated Ceps on Ramsgate with the refurbishment program, but, 7 units, the 1980s refurbished Beps, were SWD, never SED, it is then true to say as a squadron fleet they were never all Kent coast units.
Then 1990s they moved around further no need for details.