Ok - had a chance to do a reckoning of my mileage. In total, I covered around 423 miles. I left Chatsworth House with just under half a tank, so to be sure I refilled in Chesterfield before the drive home. After that, I have just over half a tank, so it's highly possible that I could have done the whole weekend on a full tank (especially if I didn’t have that queue of traffic in Chesterfield to sit in). I just didn’t want to risk it.