A quick update about my experience with the Gridserve 350kW chargers at Wetherby services. There has been speculation that powering the car down before charging might help with the car connecting to the charger:
I'd always powered down my car this way before charging on several previous visits to these chargers as, for some reason, I thought you had to power the car down for it to charge. As that always worked, I never questioned it! However, I said I'd give those chargers a go without powering down to see what happens next time I was at them.
Today was my first chance to try, so I put the car into P, got out without locking the car (my wife was still sitting in the car ready to power it down if needed!), connected the charge cable and showed the charger my card. There was quite a pause during which the charger had a message saying that it was connecting to the car. I was about to give up when the car started charging. No error messages, just quite a long handshake it seems. We locked the car to go to the services and the charge continued uninterrupted. So it worked fine without the shutdown. I'll try again in about a week's time on my way home, but I'm expecting it to be ok.