charge via EU equivalent to our home 3 pin plug, how would that work?,
240V Mains is about 5~6 MPH charge, so works OK over-weekend, and overnight will give you 70 miles or so.
A Schuko adaptor is available for the UMC (my search for Tesla Shop turns up EUR 90
and "only shipped to addresses in Netherlands otherwise call Service Centre" dunno if that has changed?), or you could buy a "beefy" Schuko extension lead (long or short
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I haven't used these people, but it mentions EV car charging and the differences between Earth in Germany & France so ...
European Schuko/French CEE 7/7 plug to 13A socket adaptor
If you haven't already got one you might want a good quality UK extension lead (plus Schuko adaptor).. I was pleased with the people I got my lead from but they don't list Schuko
13amp Heavy Duty leads
The place we stayed in France had Live/Neutral wired back-to-front, which I gather is not uncommon, and Tesla is sensitive to that, so you might want to buy a high-amperage Schuko "loose plug" and fit that to your extension lead yourself, so you can swap Live/Neutral if necessary (I have a "tester plug" which shows if wires are the wrong way round / earth fault etc.)
If anything trips, or the plugs get hot, you can reduce the charge rate (on the dashboard).
There are Superchargers in both Folkestone and Calais Eurotunnel terminals (they are tunnel-side of check-in at DEPARTURE only); there is also a small Supercharger on the French side (outside the port).
There is some (country specific) advice on Tesla site
Charging Abroad
If you have (or can borrow) a CHAdeMO adaptor that may increase your options.
If not already familiar with it suggest you try A Better Route Planner, pick your Model and the Route and see what it says for charging locations etc. In particular any stops where you will need to charge over 80% as that will indicate that they are a bit touch-and-go and if weather bad / cold you would need to reduce speed.
Am MX100D cruising at 130 KPH has a range of about 210 miles ...
What 3rd party options are there?, do I need to register an app or buy a charge card ?
Yes, I think getting cards or RFIDs / registering APPs would be a good idea, but I don't know what is best for where you are going.