Could some sort of pattern like this be worked:
Fast trains Plymouth to London: Newton A, Exeter, Taunton, Westbury, Reading, London
Two different semi fasts:
1. Exeter, Tiverton P, Taunton, Castle Cary, Bruton possibly?, Frome, Westbury, Newbury, Reading, London
2. Exeter, Taunton, Westbury...