Research by uSwitch found 1.4 million over 65s with a household income of £30,000 or less eat just one cooked meal a day to stay out of debt.

One in five, or 1.2 million people, struggle to pay their energy bills over the winter months, the survey revealed.

Two in five keep the lights off while in the house at night, while a further two in five can only pay bills if they make spending cutbacks in other areas.

Three quarters admit they have taken some kind of action to reduce their energy bills including keeping internal doors closed, only heating one room at a time and wearing a jumper or coat in bed.

Many of these people could save money on their energy bills by receiving the Winter Fuel Allowance – however, less than one in ten said they received the benefit.

Most over 65s are entitled to the payment and should receive it automatically. People have to claim for it if they do not get benefits or a state pension, or they only get Universal Credit, Housing Benefit, Council Tax Reduction or Child Benefit, or they get benefits or a state pension but live in Switzerland or an EEA country.

Sarah Broomfield, energy expert at uSwitch, said: “It’s really concerning to discover that so many elderly people are struggling to stay out of debt and keep warm over the winter.

“No one should have to limit how many hot meals they eat every day or keep their homes dark at night because they’re so worried about their energy bills that they’re put off turning the lights on at night.

“If people are meant to be automatically enrolled to receive benefits, it’s really important that they know what they’re entitled to – that way they can check if they don’t think they’ve been receiving the support they’re due.

“It’s also vital to understand that loyalty to energy suppliers will only ever leave people over-paying by hundreds of pounds a year on a poor-value standard variable tariff.”