The big energy firms have been criticised for increasing prices to one or two pounds below the new price cap.

Five of the six biggest suppliers have announced price rises from April 1 of an average of £57 a year.

The cap will rise by 6% to £1,089 a year for a dual fuel average use customer.

Suppliers E.on, EDF, Npower and Scottish Power have announced increases in their average bills to £1,088 a year. British Gas has put its up by one pound less, to £1,087.

SSE has not announced a rise yet.

The rises mean four million prepayment customers and one million vulnerable customers on the standard credit meters face a price rise from next month.

Consumer campaigners said the price cap has not offered much help to those strugg;ling with bills.

Martin Lewis, founder of moneysaving Expert.com said: “Politicians had promised energy price caps were to be the saviour of energy market rip offs. Yet in practice, what we’ve seen so far is flaccid.

“A price cap is supposed to set a maximum price for the ‘few’ firms not engaging in competition. That was never going to happen. In reality, it’s simply allowed all the big firms to say, ‘that’ll do’, and set their prices within a quid or so of the maximum.”

He said three of the big six are less than £15 cheaper than before the price cap was introduced.

He added: “So forget the price cap. The best advice for most people on prepayment meters is to do a comparison to see if there’s a cheaper tariff.”