Energy suppliers have been criticised for charging consumers who only use a small amount of energy over the odds.
An investigation by Times Money found that tens of thousands of low income households and pensioners who do not use a lot of energy have seen their fuel bills rise over the past five months, despite advertised price cuts.
The study found that price cuts were reducing bills for high users more than they were for consumers who actually conserve energy.
Low use consumers for energy suppliers Scottish and Southern Energy saw their energy bills rise by 1.5 per cent, or £10 per year, even though the company said it has cut the cost of gas by four per cent.
Audrey Gallacher, head of energy at industry watchdog Consumer Focus, said: "If companies don't pass on plummeting wholesale costs, post-increasing profits, aren't transparent and if no one can break in to their market, something is seriously wrong."
She added that the behaviour of Britain's main energy suppliers calls for serious scrutiny to prevent them from exploiting vulnerable consumers.
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