I have changed to online only, London based, So Energy – much cheaper than almost all suppliers, very pleasant helpful contact centre, though must switch online, however very easy to switch. Monthly DD can be paid using seasonal adjustment ie pay more winter/less summer or same all year round. Note that you pay in advance each month not as usual 1 month behind. 
Hope this proves useful. I’ve added all the fine details of above tariffs, etc on submit sheet.
Many thanks for all the help the website provided. Sorted for another year!
I signed up today for the So Turtle tariff. Good customer service during my enquiries. Based on 6000kWh split 2400kWh day and 3600kWh Economy 10. 12 month fixed contract, monthly direct debit. Personal projection £872 a year. Standing charge 22.05p/day, Day rate 16.02p and cheap rate 11.29p. £5 early exit fee.