The watchdog said high levels of new investment in infrastructure mean utility bills may rise significantly from current levels and will likely hit households with incomes in the lowest 10% particularly hard.

Over two-thirds of the £310bn worth of planned infrastructure is expected to be paid for by consumers through their utility bills.

But the Government and regulators do not know how much household utility bills will increase and whether bills will be affordable, the NAO said.

Ann Robinson, director of consumer policy at uSwitch.com, said: “These figures are simply shocking. The country is already on the brink of an energy affordability crisis with almost seven in ten households (69%) going without heating at some point last winter and over eight in ten (83%) saying they will be rationing their energy use this winter in an attempt to keep a lid on bills.

“Affordability has got to move back to the heart of energy policy. The Treasury has got to do a proper impact assessment to see what this means for consumers in real terms but it’s also important that we get competition working fully in the energy market. Most consumers are seriously concerned about their energy bills and the recent price hikes have only added to their woes, making almost eight in ten (78%) more worried about their winter fuel bills this year”.

Five of the big 6 energy providers have recently announced price hikes.