Alistair Darling will this week announce plans to use legal powers in stopping energy companies make a reported £400m in excess profits from some of Britain’s poorest consumers.

In what has been termed an ‘unusual intervention in the market’، Darling is expected to announce in this week’s budget a plan to control the tariffs paid by 3.8m electricity customers and 2.8m gas customers who use pre-payment meters.

The Financial Times reports HM Treasury ministers and officials abandoned ten days of talks، after they failed to persuade energy companies to ‘voluntarily’ put more money into cutting bills for poor consumers.

Darling is expected to say talks are continuing with the companies on a wider package of measures and treasury officials said yesterday that، as a first step، he would use reserve government powers under the electricity and gas acts to cut tariffs for customers with pre-payment meters، either through a cap or some other mechanism.