I would suggest you start by going the European National Railways Website, http://mercurio.iet.unipi.it/misc/timetabl.html Choose the GB timetables and then just start putting in your destinations and dates. I tried using Gatwick and Exeter and that appears to be a 4 hour trip. Click on the details button and it will show your route and all the stops. This way you can select the route you would like and minimize your number of changes. Have a good trip.

Cheer-e-o

Greg Mpls, MN