Instead , a shuttle service between Epping ( to connect with trains to London ) and Ongar was used . At one stage , it was possible to see the unusual sight of steam trains and London Underground electric multiple units side-by-side at Epping . The Epping-Ongar branch lost its through trains to London , and a shuttle service between Epping ( to connect with trains to London ) and Ongar was implemented ; for a short time , one could see the unusual sight of steam trains and London Underground electric multiple units side-by-side at Epping .