The best company which supports economy 10 would be no one but your local supplier......

I live in London locally, and though EDF s my local supplier - Southern came first to me that they support economy 10....

 I spoke to NPOWER, POWERGEN - where I was been assured that they deal with Economy 10, I got the info that they were not been promoted on discounted offers as like the standard or the internet tariffs....

 So the best option would be no one but your local supplier...............

cheers