When I was really young about 1990 I remember going from Newcastle to Plymouth on the XC route and I was sure on one occasion the usual HST service was replaced by a class 73 with MK2 stock. This is back in the days of the grey and red stripe intercity livery. I didn't know a lot about trains then only a bit of train spotting, but I'm sure it was a class 73 which is unusual as they were mainly used in the Southern region not XC because they use the third rail which is only found in the Southern region. I know the XC route used HSTs and class 47s back then but it definitely wasn't a 47. If not what other locomotive could it have been and what locos have been used on the XC route from NE to SW?