Quick question, and I really should know the answer, but why do so many (indeed is it all) mainline steam tours have to lug a diesel at the rear of the train? Is it for heating, power supply, fail safe in case the loco stalls or what? I recollect several years ago one of the locomotive owners or operators converted a parcels wagon with a built in diesel motor but perhaps that was for a different purpose. It's a shame because they are so damn ugly.