Millions of adults with pre-existing serious health issues are living in cold and damp homes, akin to the grim conditions described in Charles Dickens novels, according to fuel poverty campaigners.
Research from YouGov for the Warm This Winter campaign shows 18% of the population (9.02 million adults) are living in cold and damp homes this month.
And 26% of people with health conditions find their illnesses are made worse by cold and damp because they are unable to heat their homes to a safe standard.
The campaign said the data shows the growing depth of the energy bills crisis - especially among the most vulnerable.
Jacky Peacock, from Advice for Renters, a charity working with those in fuel poverty in north London, said: "We used to read Dickens at Christmas with a sense of nostalgia, but now Dickensian conditions are back for those who can't afford to heat their homes this winter."
The research also found that more than a quarter (28%) of those with disabilities live in cold damp homes.
It showed people are not just concerned about their own welfare - 9% of people are worried about an older relative being exposed to the health impacts of living in such conditions, and almost a third (27%) are worried about the impact of fuel poverty on their community.
Jonathan Bean, who lives in Buckinghamshire, says the mould in his conversion flat is so bad that it has spread to his clothes.
"This morning, when I went through my wardrobe, I found that my clothes are starting to mould as well," he told Sky News.
"This was my new jumper that I was going to wear today to keep warm," he said, taking out a navy blue knitted top. Light patches of mould were visible across the front and sleeves.
"It's growing mould inside my cupboard.
"I've now got to separate this from my other clothes and check all the rest of them too.
"It's pretty awful. Literally, everything is moulding."
Jonathan lives in semi-rural Ballinger Grange, where no gas lines means many households rely only on electric heaters to warm their homes.
His 16-year-old son has asthma, one of the conditions that campaigners say is made worse by living in cold damp homes.
"I let him use his heating as much as he wants but even that's not enough.
"He's wearing his coat.
"I hate seeing him revise for his GCSEs while he's shivering away," Jonathan said.
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Simon Francis, co-ordinator of the End Fuel Poverty Coalition, told Sky News: "For many people, it's not a Christmas of joy at all.
"It's a Christmas of real hardship, fighting a daily battle to keep damp from infecting their homes, and if they've got asthma, lung or heart conditions, then they're made much worse by living in these conditions.
"What will happen is these people will end up at the door of the NHS."
The campaign said that, despite government calls for people to save energy, over half (55%) of people believe they have already implemented energy reduction measures prior to this winter - with 15% already cutting back their energy use to the bare minimum necessary to keep safe.
The Department for Levelling Up, Housing and Communities told Sky News: "We are providing cost of living payments worth £1,200 to the eight million most vulnerable families to help this winter.
"This in in addition to capping people's energy bills this winter and next."
The department confirmed to Sky News that the £1,200 for eight million vulnerable families was announced earlier this year, so is not new funding.