They confirmed it again on the phone yesterday, and told me after checking with their ‘floor support’ that although they do not install economy 10 meters they are able to provide the economy 7 tariff if the e10 meter is already installed. Perhaps calling them on the phone is the best bet, and stressing that the meter is already in place. Previously when I called to ask if they supply economy 10, it was an outright ‘no’ as they assumed I meant the specific tariff and meter installation. They’ve confirmed it for definite twice when I’ve specifically asked for economy 7 supplied to an existing e10 meter.
Still waiting for my supply to switch to EDF to get the meter installed. If I am successful switching back to Scottish Power I will post an update.