Poor families are being "priced out" of heating their homes, threatening their health and well-being, a new report has claimed.
Children's charity Barnardo's said there is a "fuel gap", with the poorest families in England spending £450 a year less than they should do on heating.
Households with the bottom 10% of incomes need to spend £1,165 a year to adequately heat their houses, but are actually spending just over £700.
Chief executive Anne Marie Carrie said: "If we're serious about tackling child poverty then we need to get serious about tackling fuel poverty too. Families should never have to choose between whether to heat their homes or put food on the table for their children.
"Many of the families Barnardo's works with are bearing the brunt of companies' unfair tariffs because they are using pre-payment meters to pay off their debt and to pay for gas and electricity. Effectively these families are being penalised by their payment method at a time when they need the most financial help.
"Energy companies have a moral duty to behave responsibly by ensuring that the poorest families are on the lowest tariffs available and that prices for pre-payment meters are brought down to the same rates as online tariffs.
"Furthermore, we would urge the Government to tackle the issue of fuel poverty by the root, by bringing forward the requirement on landlords to make their properties energy-efficient for tenants."
A Department of Energy and Climate Change spokesman said: "We can't control volatile world energy prices, but we are working with the independent regulator, suppliers and consumer groups to help people keep bills down this winter, we are making sure there is more support for the most vulnerable households, and the Government and Ofgem are making major reforms to the market to help make sure we can all have affordable energy in the long term."