Mention should also be made of the small pool of locos that were reserved for taking trains from Euston Station to Wembley Carriage Sidings and from Manc Piccadilly to Longsight. I remember them using the older AC locos for that but in inter city livery, but the livery was washed out due to frequent trips through the washers. I am only aware of this practice at Man Picc and Euston. But maybe happened at Glasgow Central and Liverpool LS - I dont know for sure.
I can recall Liverpool Lime Street when we first moved from Somerset in the 1960s, that the full range of locos were used to and from the Edge Hill sidings. To the end of steam an 0-6-0T tank might bring in the stock for a Euston electric service, this might be followed by an AC electric loco bringing in the stock for a Newcastle train, which after its departure with a diesel would shunt around onto the Euston train and depart with it. Any combination.
I did write here just a few years ago about departing Euston on a Pendoline at about 9am, exactly parallel with the ecs of the Scottish sleeper, with a Class 86, the full Mk3 sleeper train, plus the incoming loco now on the tail, and that this train on the slow line kept perfectly level with the Pendolino all the way out to Kensal Green; impressive for a 50-plus year old loco.