Spent the morning on the fuel cards again and went looking at what the services actually charge, rather than what we assume they charge.
The thing that surprised me is not that motorway diesel is dear. It is how far apart the service areas are from each other. Cheapest on the network this morning was 189.9p, dearest was 226.5p. That is 36p a litre between two places doing the same job. Both of those are geography as much as anything, one is in Northern Ireland and the other is out past Inverness, so take them with a pinch of salt.
The mainland picture is still worth knowing. A fresh reading at Bolton services this morning was 218.9p, updated eight hours before I looked. The national diesel average is 196.2p. That is 22.7p a litre, so about sixteen quid on a 70 litre fill, for stopping at that one rather than coming off.
What I take from it for the vans is that the useful question is not whether to use the motorway, it is which services. If two on the same stretch are 20p apart, knowing which one before you set off is worth more than any driving technique.
The prices come from the government feed every forecourt has to report to within half an hour of a change, and all 168 service areas are listed with their latest diesel and unleaded on this page of motorway fuel prices, station by station, if it is any use to anyone.
Worth a look before a long run if nothing else.

