An interim update: I've been using the same electrician for the last few years and have some confidence in his abilities. He is of the opinion that the 100 Watt Amp looped supply may be OK to support a 7kW charger, but needs to speak to Scottish Power to get their blessing.
Meanwhile, talking to other people, it seems that installing EV chargers is the new double-glazing - the same thing that happened a few years ago with smart meters. People are getting jobs to do this with minimal training as companies seek to surf a wave of money. David might be wrong about the power supply, but I'll rest a lot easier knowing a properly qualified electrician installed the charger and RCD.