A basic 600 that runs between Leighton Buzzard and Exeter. Choose any control as a start. You might want to check that there is some kind of accommodation at around 360km from your chosen start location.
The route runs south from Leighton Buzzard, through Pangbourne to Chandler's Ford. There it turns towards Salisbury to join the A30. The next control is Sherborne. The route deviates from the A30 to run south of Yeovil. It rejoins it to run through Crewkerne, Chard, and Honiton to Exeter. From Exeter it initially follows the A38 before heading through the Somerset Levels to Wells. Before Wells there are various hotels and travel lodges that would serve for a sleep stop. From Wells the route takes you across country, through Malmesbury to Cirencester, then on to Brackley. The final leg returns to Leighton Buzzard and the finish.