Most international flights will arrive at London Heathrow but there are some flights to Bristol airport and Exeter airport. All times below are approximate.
You can either take an airport shuttle bus to Reading station (45 mins) or you can take the train in to London Paddington (30 mins). From either station you can then catch the train to Exeter St David's station (2 - 2.5 hours).
There is a bus service to Exeter (2 hours) or you can take the airport shuttle bus to Bristol Temple Meades station (30 mins) and catch the train to Exeter St David's (1 hour).
There is a bus service to Exeter (30 mins) or taxis.
There are direct services from London Paddington and London Waterloo (the route from Paddington is significantly faster) to Exeter St David's, which is the main station for Exeter and a 20 min walk from the University campus. Eurostar trains link London St Pancras to Brussels, Paris and Amsterdam. Travel between London stations is easiest using the Tube network.