Did a very similar run in 2001 with a friend, in a single day, but topped and tailed with a round of golf at the most southerly and northerly courses on mainland UK. Took us 20 hours in total, but we did stop for lunch and refuelling a couple of (a few) times. Our golf was poor at the start of the day (0400) and total rubbish after being in a car for the best part of 15 hours. We had to rely on handwritten notes to 'remind' us where the speed cameras were.
