Ofgem has fined the energy giant for charging an unfair amount to many of its customers, simply because they paid using a different method.

ScottishPower was fined £750k for varying its prices too much depending on the payment method

Energy company Scottish Power is the latest of the Big Six to be fined by Ofgem, following an investigation by the industry regulator.

Utility companies can charge different amounts to customers depending on their payment method, but the difference must reflect the true cost of providing the service.

Scottish Power was found to not have the correct systems in place to calculate the right price for each payment type, and was charging customers unfairly.

If you pay by Direct Debit it will be cheaper than being invoiced quarterly and paying by cash or cheque.

A Scottish Power spokesman said: “Scottish Power has co-operated fully with this investigation. We recognise that historically we did not have a robust process in place but we are pleased that Ofgem has concluded its investigation and made no finding that any specific impact on customers resulted from our failure to have these processes in place.”

“We fixed this problem by December 2012 and all of these processes are now fully compliant.”