The Big Six energy giants have been accused of "getting away with green murder" as only two providers, British Gas and SSE, said they would pass on savings to customers from a government overhaul of green taxes.
EDF Energy and E.On said they took Government cuts to green levies into account when they announced reduced price rises. However, both said that current customers on fixed price contracts would miss out on the saving, claiming they already enjoy a discounted rate.
Npower has committed to not raise prices again until 2015, while Scottish Power has said it will pass on the proposed saving, however experts say it would only apply to variable rate standard customers.
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Chancellor George Osborne confirmed plans to roll back government green schemes in his Autumn Statement, which would save households around £50 on average.
Moneysupermarket editor-in-chief Clare Francis said: "The reduction of green levy commitments for UK energy providers showed all the signs of being a good thing for struggling households who expected to see it reflected in their energy bills.
"However, indications are that not everyone will win in the war on the cost of energy and some will essentially lose out because they were savvy and switched to pay less in the first place.
"We feel this is unfair as these customers are in effect overpaying on the reduced levy whereas others are paying their fair share. Energy companies should evenly reduce the cost of green levies for all customers, and not have a selective approach as to who will get a reprieve. After all, the Big Six blamed the Government levies to justify inflation busting price increases.
"For the many customers who signed up to a fixed tariff prior to the recent price rises to safeguard their household from the threat of rising prices, the green levy will have been built into the costs, and should now be reduced accordingly.
"Our advice to customers on fixed rate deals is to stay put as their existing tariff is still likely to be cheaper than the products currently available on the market. However, if you are on a fixed rate deal without any exit penalties, it is worth comparing prices once all of the changes take effect as there may be further savings to be made.
"Against a background of rising prices, £50 might be small but when times are tough every little helps. British Gas and SSE must be congratulated for taking this approach, and we would ask that all other providers do likewise."