ra il ▁network ▁since ▁ 1 9 8 3 , ▁and ▁continue ▁to ▁do ▁so , ▁now ▁ref urb ished ▁by ▁Al st om ' s ▁East le igh ▁Works . ▁The ▁Class ▁ 5 0 8 ▁unit ▁is ▁now ▁ ▁years ▁old , ▁making ▁them ▁among ▁the ▁oldest ▁units ▁still ▁in ▁service ▁on ▁the ▁UK ▁main land ▁rail ▁network , ▁after ▁the ▁Class ▁ 3 1 3 ▁and ▁Class ▁ 5 0 7 . ▁ ▁Description ▁The ▁class ▁was ▁developed ▁for ▁Mer se ys ide ▁following ▁extensive ▁tri als ▁and ▁testing ▁of ▁the ▁ 4 P ep / 2 P ep ▁stock ▁built ▁in ▁the ▁early ▁ 1 9 7 0 s . ▁Test ing ▁of ▁Class ▁ 3 1 3 ▁took ▁place ▁on ▁the ▁Northern ▁Line ▁on ▁Mer se ys ide , ▁using ▁ 3 1 3 0 1 3 / 0 6 3 ▁which ▁were ▁loan ed ▁from ▁the ▁Great ▁Northern ▁Line ▁of ▁the ▁Eastern ▁Region ▁to ▁Hall ▁Road ▁dep ot . ▁Original ▁plans ▁were ▁drawn ▁up ▁for ▁ 5 8 ▁Class ▁ 5 0 8 s ▁to ▁be ▁constructed , ▁although ▁cost ing ▁issues ▁limited ▁the ▁event ual ▁number ▁to ▁ 4 3 . ▁However , ▁following ▁planning ▁and ▁building , ▁British ▁Rail ▁decided ▁to ▁di vert ▁the ▁ 5 0 8 s ▁to ▁work ▁alongside ▁much ▁older ▁first - gener ation ▁ 4 Sub ▁EM Us ▁in ▁the ▁London ▁Water lo o ▁area . ▁The ▁first ▁unit ▁was ▁delivered ▁to ▁St raw berry ▁Hill ▁dep ot ▁on ▁