Apologies if someone has already mentioned it, but the prototype EM1/Class 76 ran in Holland whilst the Woodhead route was being built. it was the Dutch who gave the loco the name "Tommy".
Also no one has included the Metropolitan Railway's 1863 A Class 4-4-0T locos. These were to a design originally intended for the Tudela & Bilbao Railway in Spain, and were ordered by the Met after the GWR withdrew its locos and rolling stock. Not just a case of a British designed loco working overseas, or of a loco being exported once it was surplus to requirements in Britain, but a design that operated from new in both countries at the same time.