I think loosely speaking the definition of intercity, is Long Distance, 100mph and above, frequent service, First class, the routes to Me are:
London-Plymouth-Penzance,
London-Bristol-Swansea,
Euston-Birmingham-Manchester-Liverpool-Chester and Holyhead-North West and Glasgow,
London-Leicester-Nottingham-Sheffield,
London-Leeds-Hull-North East and Edinburgh,
London-Ipswich-Norwich
Penzance-Plymouth-North West and North East and Bournemouth-Southampton-Reading-North West and North East,
Trans Pennine Express, London Commuter routes including Weymouth and Exeter via Salisbury, anything non virgin or Caledonian Sleeper on WCML, anything on Cross Country operated by 170’s are to me not Intercity, I know there is blurring of the definition of what’s is or isn’t Intercity, I go by the traditional BR Intercity branded routes up to privatisation, which were mk2-mk4, First class and buffet at minimum, some with Pullman dining, generally speaking were faster and had a better level of on board service compared to Regional trains.