I popped into Marks and Spencers the other day and someone was touting for business for m and s energy, which is run by Southern Electric, Scottish Hydro Electric or SWALEC depending on where you live.
I am already with Southern Electric, so signed up to m and s energy, which leaves me on exactly the same tariff, same account number, same payment details etc. but I now get £20 M&S vouchers and will get another £10 now I've signed up to paperless billing.
So £30 vouchers for changing from Southern Electric to Southern Electric! I even have to go onto the Southern Electric website to access my online account!
I did this instore, but it looks like you can easily do it online as well