Nearly one in four adults plan never to turn their heating on this winter, polling suggests, as average bills are set to rocket while the temperature drops.

This figure is even higher for parents with children under 18, according to a Savanta ComRes survey carried out before the new price cap was announced.

The pollsters asked more than 2,000 UK adults how they would respond to increasing energy prices over the winter – 23% said they would not turn their heating on at all, rising to 27% among parents with under-18s.

Seven in 10 (69%) said they would switch their heating on less, and one in 10 (11%) said they would take out a loan, with the latter figure rising again for those with children under 18 (17%).

It comes amid resounding warnings that people are in for a dire winter, with the energy price cap set to rise by 80% by October, pushing the average household’s yearly bill up from £1,971 to £3,549.

Chancellor Nadhim Zahawi has said he is working “flat out” to draw up options for a plan of action for the next prime minister so they can “hit the ground running” when they take office in September.

But some say the Government has been missing in action, while neither Tory leadership candidate has set out in full how they would help people ahead of the contest’s conclusion.

The Liberal Democrats, who commissioned the survey, warned families are being forced to make “heartbreaking decisions”, with the country “on the brink of the worst cost-of living-crisis in a century.

The party is calling for ministers to scrap the energy price cap rise in October, funded partly by a further windfall tax on oil and gas companies.

The polling, which was conducted between July 29 and July 30, also suggests that parents of under-18s are increasingly likely to put more on their credit card due to rising energy bills (33% compared with national average of 23%).

The survey results were weighted to be representative of the UK by age, sex, region and social grade.

Christine Jardine, the Lib Dems’ Cabinet Office spokeswoman, said: “Families and pensioners across the country are making heartbreaking decisions because the Government has failed to save them.

“It is a national scandal that parents are having to choose between heating their homes and feeding their children. It shouldn’t be like this.

“Britain is on the brink of the worst cost-of-living crisis in a century and yet still Liz Truss and Rishi Sunak will not scrap the energy price rise. It is clear energy prices must not be allowed to rise in October.”

Ms Jardine said an “economic catastrophe” is now “just a month away”, blaming a “zombie Government in Westminster, and two leadership contenders living on another planet”.

“It is time to tax the record multibillion pound profits of oil and gas companies and use the money to save British families and pensioners,” she said.

A Government spokesperson said: “We know people are incredibly worried about rising energy bills, following unprecedented gas prices across the continent driven by global events, including (Vladimir) Putin’s aggression in Ukraine and his weaponisation of energy in Europe.

“Direct support will continue to reach people’s pockets in the weeks and months ahead, targeted at those who need it most like low-income households, pensioners and those with disabilities.

“As part of our £37 billion package of help for households, one in four of all UK households will see £1,200 extra support, provided in instalments across the year, and everyone will receive a £400 discount on their energy bills over winter.

“The Civil Service is also making the appropriate preparations in order to ensure that any additional support or commitments on cost of living can be delivered as quickly as possible when the new prime minister is in place.”