I have a referral code for OVO energy for a £50 M&S, John Lewis or Amazon voucher, if anyone is interested? PM me if you would like it.
I've found their customer service to be excellent and efficient, the best experience I've had with any of the energy suppliers. Best of all, they pay 3% interest on credit balances (4% in the second year, 5% in the third year) so if you pay in 12 equal monthly instalments, you will earn interest during the summer months when you are using less energy.