'Don't take price increases lying down' 218,000 households face a price rise this month

"This loyalty tax is unfair and hits vulnerable and elderly customers the worst.

"As a loyal customer, you should never be charged more, whether it's for a coffee, the weekly shop or your energy bill, which is why at Bulb we don't use hidden charges or penalise loyal customers for staying with us.”

Elsewhere, bill-payers have been warned they could be among 13 million households who are owed a total of £1.8billion in credit balances.

Among them, more than one million are due more than £300, according to new research from Uswitch.com.

Sarah Broomfield, energy expert at Uswitch.com comments: “At a time when many people’s finances are stretched any windfall would be gratefully received.