You should check which tariff EDF have you on. The flats are designed (I believe) to draw power on the basis of Economy 9 (i.e. 9 hours of cheap rate electricity). My bills are no more that £150 per quarter and I am on this tariff (one bed flat).
When I moved in, I was incorrectly put on Econ7 by EDF. I highlighted that this was not the case for the other customers in my block and they transferred me. This could be why you're paying so much.