The companies responsible for the UK's and networks pocketed a near £4billion windfall from household bills during the energy and cost-of-living crisis, a report has said.

Citizens Advice said the energy network companies which provide pipes and cables to people's homes have taken a staggering £3.9bn in excess profits over the past four years after the industry regulator misjudged their costs.

The charity said a misjudgment by has allowed energy networks to profit from the high inflation which fuelled the cost-of-living crisis.

Dame Clare Moriarty, Chief Executive of Citizens Advice, said: "We now know that while households have struggled with sky-high energy bills, network companies have been making astronomical profits.

"We've called out the billions of pounds of excess profits made by these companies before, and Ofgem said it would get tougher in subsequent price controls. The measures it put in place have clearly failed."

She urged networks to do the right thing and give the money to struggling billpayers by funding "much-needed" debt relief and targeted energy bill support.

Citizens Advice said a flaw in Ofgem's current price control which it warned the regulator about in 2020 has rewarded companies with billions in undeserved profits, leaving customers without a "fair" deal.

The charity said those profits are "over and above" what Ofgem believes is reasonable. It added average bills are now more than two-thirds higher than they were in 2021.

A spokesperson for Ofgem said: "After a wide and public consultation, we decided to adjust our price controls going forward so that such inflation shocks do not lead to any excessive financial overperformance.

"We have also made clear that network companies can and should use the temporary effect of higher inflation to strengthen their balance sheets to benefit consumers and support those who need it most."

The Energy Networks Association (ENA) said Citizens Advice's analysis is overly simplistic and looks at a narrow two-year period, ignoring the longer investment timeline and balance of returns across a five-year period.

An ENA spokesperson said: "Electricity networks are bringing in private investment of more than £100bn between 2021 and 2031, investing in our grid to promote growth in our economy. It's crucial to keep the regulatory environment stable during this time."

They added that the UK has one of the most reliable grids in the world and that running and upgrading the electricity networks costs about 48p per day on the average bill.

Citizens Advice insisted network companies benefited from borrowing costs being overestimated in the current price control because of high inflation. It said this has boosted company balance sheets, dropping the multi-billion pound windfall into their laps.