This is a linear route, so you will have to plan your journeys accordingly.
Exeter St David's Railway Station/Wells/Durrington/Stow-on-the-Wold/Buckingham/London Marylebone Station.
Here is the calendar routesheet. Read it even if you intend to use gpx.
Here is the gpx track. Controls are waymarked. Note that rerouting via another app will probably cock-up the route through Wells (it goes over a footpath to pass the Cathedral).
Long-distance cycling under AUK rules is often (though inaccurately) referred to as audaxing. Mudguards are not required for any of these events. Use whatever bike suits you. If you don't want to follow a routesheet then download the GPS file. You will need to be fit and self-sufficient. Most of these events, especially the longer ones, are hard. You should be an experienced cyclist with both fitness and stamina. There is a minimum speed of 15kph for all the events of 200km and above. Don't worry about the maximum speed of 30kph, you won't get near it. Prepare your bike and yourself carefully for any of these events. If you do all the distances, you become an Exeter Wheelers Super Randonneur.
This weather forecast is generated by the Met Office Weather Widget
Click 'Options' to change location
Useful or entertaining, or both.
Guide to AUK events from http://h2g2.com