The Southern Railway ( SR ) gave the designation 2Bil to the DC third rail electric multiple units built during the 1930s to work long-distance semi-fast services on the newly electrified lines from London to Eastbourne , Portsmouth and Reading . The Southern Railway ( SR ) gave the designation 2-BIL to the DC third rail electric multiple units built during the 1930s to work long-distance semi-fast services on the newly electrified lines from London to Eastbourne , Portsmouth and Reading .