Housing charity Shelter has called on the government to build 90,000 good-quality social homes a year.
It commissioned a survey which suggested that around a third of adults do not have safe or secure homes, based on criteria including whether the accommodation had enough bedrooms, was mouldy or structurally unsound.
Shelter calls it a "housing emergency".
The UK government said it is spending £12bn over the next five years on affordable housing.
And the Welsh government said it had invested £2bn over the last Senedd term to exceed its target to deliver 20,000 affordable homes.
The Scottish government said Scotland had "led the way across the UK with almost 100,000 affordable homes delivered since 2007 and we are committed to delivery of a further 100,000 by 2032".
Over the course of a week last month, Shelter, via polling organisation YouGov, asked 13,000 people about their home and housing experiences and combined the results with government data on homelessness to calculate that 34% of adults in Britain did not have safe or secure homes.
People were defined as being affected if they agreed with at least one of the following statements:
- I do not have enough bedrooms in the home, meaning there is a need for unsuitable room-sharing (eg between siblings of the opposite sex)
- My home has significant mould, condensation or damp problems
- I cannot keep my home warm in winter
- My home has safety hazards such as faulty wiring, fire risks, or hazards that could cause a fall
- The home I live in is not structurally sound
- I regularly have to cut spending on household essentials like food or heating to pay the rent/ mortgage
- I worry that I might lose or asked to leave the home I am currently living in
- Thinking about the home I currently live in, I found it hard to find a safe, secure and affordable home as I experienced discrimination because of my race, gender, sexuality, nationality, or religion
Shelter said black people were 70% more likely to be affected by housing issues or homelessness than white people, while Asian people were 50% more likely.
Its survey also suggested that more than half (54%) of people with a significant disability did not have a safe or secure home, compared with 30% of people without a disability.
And nearly two-thirds (65%) of single mothers did not have a safe or secure home under the criteria, it said.
The charity also found that 23% of the people it surveyed were living in homes with significant damp, mould and condensation, or cannot keep warm in winter, while one in 12 reported that they were regularly cutting back on essential items to pay their housing costs.
Shelter chief executive Polly Neate said: "Decades of neglect have left Britain's housing system on its knees.
"A safe home is everything, yet millions don't have one.
"Lives are being ruined by benefit cuts, blatant discrimination and the total failure to build social homes."
A Ministry of Housing statement said it was "unacceptable for people to live in unsafe accommodation" and said the government had given councils stronger tools to crack down on rogue landlords as well as announcing reforms to support tenants, including its charter for social housing residents".
They added it was providing £750m this year to help tackle homelessness and rough sleeping.
Labour's shadow housing secretary Lucy Powell said Shelter's report came as no surprise "after a decade of neglect and failure by ministers on housing".
She said the Covid pandemic had shown "deep inequalities in our housing system", with those in insecure, overcrowded homes more at risk of the health and economic impacts of the crisis.
A Welsh government statement said legislation on tenancy laws, due to come into force around spring next year, would require landlords to ensure the properties they rent are "fit for human habitation, tackling the poor conditions in some rented properties".
"We are now looking to build a further 20,000 new, low carbon social homes and will be announcing further details shortly," they said.
A Scottish government spokesperson said it would carry out an audit of its housing and homelessness legislation to ensure it met the needs of everyone and said its Housing to 2040 report outlined its long-term housing strategy.
In a statement the Department for Communities in Northern Ireland said communities minister Deirdre Hargey had begun the "biggest reform of social housing in over 50 years", which included building more homes with 2,403 social housing starts in 2020/21 - the highest annual figure for more than a decade.
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