Thanks for the info, I contacted Good Energy to clarify. They do still support E10 but it seems some of their phone staff don’t have the right info. Always worth asking for a manager or phoning back to speak with another person if you don’t get the right answer first!
email from Good Energy 19/9/18 below:
Thank you for getting in touch. Yes, we do still offer Economy 10 tariffs.
If you’d like a quote, please could you provide your full address and your annual usage in kWh’s (kilowatt hours) split between your peak and off peak times.
I hope to hear from you soon.