One in six Britons are taking "drastic action" to cope with heatwaves, including sleeping in kitchens, missing work, or booking hotels, Citizens Advice has found.
These measures extend to sleeping in gardens or on balconies, taking sick days or unpaid leave, and paying for hotels.
Extreme heatwaves this summer have put lives at risk, sparked wildfires and forced millions into hosepipe bans.
July, with temperatures above 34C, was the driest month on record for England and Wales, the Met Office confirmed.
The charity warns millions across the UK are "trapped in homes they can’t cool", with almost half (44%) feeling powerless to prevent their houses overheating.
A further four million have resorted to makeshift solutions like taping tin foil, cardboard, or damp sheets to windows.
The study attributes this struggle to poorly designed homes, which act as "heat traps", and the high cost of cooling equipment such as air conditioning, leaving people helpless.
Citizens Advice is now demanding government action on a "now year-round crisis" of "soaring heat in summer and unaffordable energy bills in winter."
Half (51%) of tenants – including those who rent privately and those in social housing – felt they lack the basic control needed to stop their homes overheating, compared with 40% of homeowners, the poll found.
The study also found 90,000 heat network consumers were unable to turn off their central heating even in summer.
Citizens Advice chief executive Dame Clare Moriarty said: “For far too many people, a summer heatwave doesn’t mean enjoying the sun – it means being trapped in a sweltering home with no control over the temperature.
“We’re now facing a year-round crisis, where poorly designed housing stock is acting as a giant heat trap in summer and as an ice box in winter.
“The Government has a vital opportunity to help fix this through the Warm Homes Plan. By investing in better insulation, ventilation, and heat network upgrades, we can ensure people’s homes are warmer in the winter and safer and cooler in the summer.”
Yonder surveyed 2,105 UK adults between July 1-2.
Rain, showers and lower pressure could soon bring some relief in August.
Following another heat spike this week, temperatures are forecast to cool down to peaks of just 22C on Thursday in London and 17C in Glasgow.
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