I’ve gone with Green Energy in the end. Their standing charge is more than others, but their off peak rate makes it very worthwhile for us. It is a variable rate, so I’ll have to keep an eye on it. iSupply was cheapest for us, but I’ve not heard good things about their customer service lately and thought with an E10 meter my switch might end up being a hassle if I couldn’t contact them! So I went with Green Energy as they were second best and very helpful.
n.Power told me they don’t have an E10 tariff.
I’ll be interested to see the spreadsheet of every else’s results when it’s finished.