Long Journeys in one of these
Looking at Tesla's page on Superchargers, it takes at least 30 minutes to get another 170 miles in the batteries, or 75 minutes for a full charge.
That's a long time to be stuck at, say, Northampton Services on the M1.
Service Station Economics: Pile it High, Sell it Expensive, Make it Quick
There's a limit to how much money anyone is going to spend in a motorway services, no matter how rich they are. Motorway services are, by definition, the very last place on earth that anyone wants to be. So the fuel, food, everything is quite expensive, and they don't bother trying to do anything to make you stay. They know you're not going to stop there for a three course meal, so they don't bother offering one. Everything they do is about getting as many cars parked as quickly as possible, toiletted, watered, snacked and fuelled as quickly as possible.
Car Charging Isn't Quick
But if everyone starts turning up in electric cars and plugging them in for 30 - 75 minutes, that's going to hog a lot of car parking spots, but I can't see what the Services can do to induce people to spend enough money to offset the reduction in the total number of people that can pass through.
Sure, if everyone had an electric car then everyone would be stopping for a long time, so opening up a decent restaurant and serving nice three course dinners would make sense. But in meantime the Service station operators are not going to want to lose too many parking spots to low revenue earning electric car charging points.
So there won't be that many points available at any of them.
From the Driver's Point of View
And can you imagine anything worse on a journey than arriving at the Northampton Services and discovering that you're going to have to wait 75 minutes for a charging point to become free before you can plug in yourself? Can you imagine what 2.5 hours there would be like?
From the Electrical Engineer's Point of View
A Tesla Supercharger runs at 120kW. That's a lot. If there were, say, 100, charging points in use simultaneously that'd be 12MW. Somewhere like Exeter Services seems to have around about 300 parking spots, so about 36MW.
I seriously doubt that any service station has a mains electricity cable fat enough to carry anything like that much power. Laying one in would be an enormously expensive proposition. To provide fast charging points for every parking spot in a large motorways services they're going to have to do something radical to its electricity supply.
Doesn't Make Much Sense
To give you an idea of how much electricity that is, Dungeness B nuclear power station is 1230MW. On its own it could run around about 30 service stations each with 300 Supercharger points, but that's still only 9000 vehicle being charged at any one time. That's a pitifully small number of cars.
If Tesla expect a mass market for people going some place, probably all at the same popular time of day, plugging their car in whilst they pee, eat, shop or otherwise entertain themselves, then they're going to have to do something radical about the number of power stations in the country and the capacity of the electricity grid to deliver large amounts of power in a short period of time. There seems little prospect to me of that scale of engineering problem being tackled anytime soon.
Charging up at home
The only way electric cars can even begin to start making any sense at all at the moment is if they're charged up slowly overnight and never charged during the day. That's much easier for a National Grid to cope with.
Claiming full UK coverage for charging points is fairly misleading. If the smallest charging location has, say, 10 outlets, then there is full UK coverage for only 10 Tesla drivers at any one time. If an 11th Tesla turns up, they're gonna have to wait. And as we've seen in California, people inconvenienced by a lack of an available outlet at a charging station seem to behave quite badly.
That's understandable; if I arrived at Northampton services on the last whisps of electricity in the batteries and discovered I was going to be stuck there for several hours whilst some other drivers took on a full charge, I'd be tempted unplug them and sneak a few minutes of charging just to get out of there.
And that's before the kids on a school excursion unplug all the cars at the motorway services for a laugh.
Saying that there's "Full Uk coverage" is just a way of persuading the mugs who don't actually have to get places to buy Tesla cars.
Knowing that most of the UK public are far from stupid and are perfectly capable of foreseeing the horrors of being stuck at a motorway services, I fully expect to see these supercharger stations getting very little use.