LONDON Eurostar said Wednesday it will run double-decker trains through the Channel Tunnel for the first time, as it faces potential competition on its routes between London and mainland Europe. A 2.0-billion euro ($2.3-billion) investment in up to 50 electric double-decker trains built by French group Alstom could help Eurostar reach 30 million annual passengers by the new decade, up around 50 percent from current traveller numbers. It comes as other European operators are eyeing the cross-