The sleepers needed ETH once the MarkIII sleeping cars were introduced. Class 47s were used: towards the end they were twin fuel tank locos that could work between London and Aberdeen without a loco change.
After the Deltics finished, daytime ECML loco hauled trains disappeared very quickly. By May 1982 only the Cleethorpes was still loco hauled and that went HST in May 1983.