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Gusman Although self-service has been almost universal in UK filling-staions for years, pre-payment pumps, fitted with card-readers, seem fairly new here. It does srtop drive-away theft by being impossible to defraud, but it also allow 24-hour service without needing pay someone to sit in the shop all night for hardly any customers.
The service-areas on the motorways stay open but most of those have reasonable numbers of customers throughout the night - and they all charge significantly more for the fuel than do the garages on the ordinary roads. **
Back in the 1960s-70s, some filling-stations installed pumps with bank-note takers, usually set to accept a single £5 note. That might have given 4 to 5 gallons. Those ended as the cost of fuel rose. £5 will not buy much petrol now, at around £1.40 / litre (£6.35 / UK Gallon, but fuels are sold in litres). Diesel fuel is more expensive still though a Diesel car is significantly more fuel-efficient than its petrol equivalent: e.g. around 60mpg v. 45mpg.
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** A Diversion:
I don't know if anyone has actually analysed fuel costs between A-road routes and motorways where a geographically-sensible choice exists.
Excepting frustrating stop-go progress due to accidents or break-downs ahead; using the motorway involves very little driving below top-gear, manual or automatic. You can generally maintain the car's optimum cruising speed (while obeying the 70mph or any temporary, lower, speed limit!), and there are none of the ordinary roads' normal obstacles - tight bends, steep hills, slow vehicles, multitudinous junctions, towns, etc.
Even passing 20 miles of road-works at 50mph adds merely 6 minutes to the 70mph time, although it feels interminable. This was the case on M6 in Cheshire for months last year, by the "upgrading to managed motorway" work.
So despite the higher mean speed on the M-way your vehicle can be at its most efficient for most of the way.
Therefore, even if you buy all of the fuel at the over-priced motorway services, and despite the higher mean speed, overall a long journey cost might be comparable or even lower on the M-way. And the journey would be quicker.
