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Best thing to do is to take your usage (kWh is best, £ is possible) and current tariff details and plug it into here. They'll tell you the best they can find (and they have a huge range), as well as emailing if something better comes along in future. They occasionally have specially brokered deals which are excellent (I have a 1y fix with British Gas for an annual cost significantly below the best of the rest). And it's free.
Time to renew our gas/elec... Greenstar (current supplier £50p/m) have offered a fixed 12 month one at £630-ish per year.