A train depot in east London holds the key to more trains running between London and the Continent, it has been revealed.Sir Richard Branson's Virgin Group and the Spanish-led consortium Evolyn both want to set up rival operations to Eurostar and operate passenger services between St Pancras and mainland Europe via the HS1 high-speed line to the Channel Tunnel.However this would require them gaining access to the Temple Mills depot in Leyton - said to be the largest train depot in London - used by Eurostar to stable and maintain its trains.