Ben, I am on EDF and my annual usage from Aug '10 to Aug'11 was 1490Kwh for a charge of £172.29. 2 Bedroom flat. Economy 9 Tariff DD, unit prices day 13.92p and night 5.36p.
Usage can be a big factor, in '09 to '10 my usage habits were necessarily different and my bill then was £413.84 for the year, still well below your bill for the last qtr.
I looked into the different tariffs and have found EDF to be the most cost effective.
Hope that helps.