I've done quite a few long journeys of up to 220 miles in one stint, knowing that I'll be charging overnight at the destination using either 13amp or 32amp. But as a backup I usually work out where the nearest 32amp or 70amp sites are … just in case. I've only ever needed a mid-journey top up on half a dozen occaisions. There are numerous websites for this, such as from :-
Home - Zero Carbon World
The 32amp / blue commando outlets can only be used if you've purchased a UMC cable from Tesla or made one up somehow. These charge up at the rate of about 25+ miles an hour.
The 70amp HPC chargers all have a dedicated cable attached, so you pitch up and plug in. They recharge the battery at about 60 miles an hour of charge (depends on your watts / mile usage).
I've often used the HPC located at the Castle Hotel, Taunton, M5. I've rolled up, plugged in and gone and had a meal in their restaurant.
The other HPC I've used a couple of times is at the Nottingham Belfry, just off J28 on the M1. But they tend to lock the box its attached to, although the receptionist will give you a key, and they've got a bar/restaurant right opposite the entrance.
If a charge point mid journey is critical, then I suggest calling beforehand just to make sure its all working....
Also, whilst I haven't yet done this, Ecotricity are gradually rolling out 32amp Mennekes charge points at all Welcome-Break motorway service stations, but you need to get the Mennekes adapter for this, and check the website for which locations have been commisioned - although I've seen some posts on the Leaftalk forum about 2 sites which appear to have had some teething problems.
If you're going to do some really long journeys get familiar with Range-Mode, and how the Estimated and Ideal range indications behave. One thing to bear in mind is to resist doing 95+mph up a motorway ... as the range will drop significantly to something like 120-140miles. If you want to maximise the distance just take it easy on the accelerator and do 60-70 on a motorway, or better still move with the traffic on major A roads where the average speed is more like 50-60mph, and if things are getting critical - go a bit slower !
Many UK owners have written up their first long journey, and the links below should provide a good insight as how they got on :-
A Range Test across the UK ..
A weekend in the English Lake District with a Roadster, UK HPC, Zero:Net, and OVMS
A Very British Road Trip (or 2010 Roadster Sport: A Space Odyssey, if you prefer))
Official HPC Charger Map for CH, DE, IT, AT, UK
Good luck with your first trip, and write it up when you get back !