 The DR connected to the MR ( now the Metropolitan line ) at South Kensington and , although the two companies were rivals , each company operated its trains over the other 's tracks in a joint service known as the Inner Circle . On 1 February 1872 , the DR opened a northbound branch from its station at Earl 's Court to connect to the West London Extension Joint Railway ( WLEJR , now the West London Line ) at Addison Road ( now Kensington ( Olympia ) ) . From that date the Outer Circle service began running over the DR 's tracks . The service was run by the North London Railway ( NLR ) from its terminus at Broad Street ( now demolished ) in the City of London via the North London Line to Willesden Junction , then the West London Line to Addison Road and the DR to Mansion House – at that time the eastern terminus of the DR. 
