British consumers are in debt to energy providers to the tune of half a billion pounds, a 9% increase on 2014, figures out today show.

Almost four million UK households are in debt to their energy supplier, with the average amount standing at £130 per home, according to price comparison and switching service

The £507m debt bill (€697m, $778m), £43m more than in 2014, comes despite a 25% fall in wholesale gas and 18% cut in wholesale electricity prices.

Ann Robinson, director of consumer policy at, said: "This is evidence that energy has become totally unaffordable for millions of homes. Disposable incomes may be on the up, but people are still under relentless pressure just to cover the cost of essential bills."

uSwitch added debt has soared despite over half of energy consumers rationing their energy use to keep bills down, an increase in disposable incomes and recent price cuts to the cost of standard tariffs. The higher levels of debt are also linked to increased energy consumption following a cold winter.

The average annual fuel bill now stands at £1,237, with 4.5 million households classed as "fuel vulnerable", spending more than £1 in £10 of their income on energy.

The UK's "Big Six" suppliers – SSE, British Gas, Npower, EDF, E.on and Scottish Power – have come under increasing pressure to slash bills after new Energy Secretary Amber Rudd wrote to energy bosses demanding they pass on falling costs to consumers.

At the end of May, SSE reported a 50% rise in profits to £369m with the remaining five energy giants also expected to report big increases later in 2015. uSwitch is renewing calls for suppliers to make double-digit tariff price cuts, better reflecting the reduction in energy costs.

"Energy suppliers must urgently pass on double-digit reductions to their customers – many of whom have admitted to going cold this winter in an attempt to keep their bills down," Robinson added.

The figures come just a week after reports that 97,000 gas and electricity pre-payment meters were forcibly installed in homes in 2014 due to customer debt. Suppliers can by law install a pre-pay meters when customers run up debt.