This reply for LP. Yes, I am in the Hamphire (old Southern Electric) area and I managed to switch to E10 with EDF from Superdeal with SSE in Nov-2015 (had to go through the EDF Complex metering section – who were quite efficient).
The actual switch to (the superior E10 rate) took until Feb-2016 to complete properly i.e. old and new suppliers billing issues sorted (due in my view to obstruction by SSE).
And I have not changed again even though EDF prices have gone up by 11% (as it is still cheaper than SSE Superdeal was in 2016).
[Note:- But knowing what I know now, and if I had to do it again :- I would try to swap from Superdeal with SSE to E10 still staying with SSE, and when – and only when achieved – then try to switch to EDF E10].
Hope this info is of use. (it/11apr17)