After hiking gas and electricity prices on their metered services, Scottish Power, npower and Powergen have all charged customers more for their bills retrospectively.

Around 700,000 prepayment customers have suffered as a result, the MPs found.

The problem apparently arises through the companies’ inefficiency. If providers hike costs but fail to adjust their meters accordingly, the customer is only charged the correct amount later, through ‘backcharging’.

The motion to condemn the practice was brought before parliament by Labour MP Brian Donohue and supported by 131 of his colleagues.

“It is simply unacceptable that these three huge companies still insist on penalising low income consumers by forcing them into debt,” Mr Donohoe told the House of Commons.

Meanwhile, energy switching advisers SimplySwitch advised customers to ask for a transfer from the outdated prepayment meters to a standard credit meter.

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