Benefit change: Tenants outnumber available Wales homes
There are not enough suitable homes available for tenants in Wales who opt to downsize amid changes to the benefit system, BBC Wales research shows.
Tenants with spare rooms face a cut in welfare payments under the so-called "bedroom tax" unless they move to a smaller property.
But figures show there are too few one-bedroom properties in Wales available for tenants who opt to downsize.
However, the UK government said it was bringing "fairness back to the system".
Tenants with spare rooms will lose 14% of their housing benefit if they have a spare room and 25% for two.
The choice for tenants has been either move to a smaller home or lose benefit - what opponents call the "bedroom tax". But it is now known that smaller properties within social housing are very scarce.
Dennis Tranter, 43, lives in the family home on the Cefn Golau estate near Tredegar, Blaenau Gwent, where he lived with his mother and father and six brothers and sisters.
His mother died last year and he has two spare rooms which means he is expected to move house or face a 25% cut to his housing benefit.
"It would be devastating [to move] because I've been here all my life basically," he said.
"I've built a home here and I don't want to give it up. I know everyone and they've grown to know me. The neighbours are tidy and I get on with everyone up here."
He said it would be a struggle but he would give up £20 from his housing benefit if he had to.
Local authorities say that across Wales there are more than 28,000 households in social housing considered under-occupied because of spare rooms - but just under 400 one-bedroom homes to move to.
The vast majority of people affected by the change are people with children who have grown up and left home, which means most need only a one-bedroom property, according to the new system.
In four council areas - Ceredigion, Blaenau Gwent, Monmouthshire and Torfaen - there are no one-bedroom houses available with local housing associations.
There are also long waiting lists for social housing. Across Wales, 70,000 families or individuals are waiting.
John Puzey, of Shelter Cymru, said the expectation of the policy was that tenants who, for example, had seen their children grow up and move away would move into smaller houses.
But he said the figures from BBC Wales showed there was nowhere for many of them to go.
Mr Puzey is concerned about the effect on estate communities of long-standing residents leaving.
"We are talking about people here who have lived in these communities for a long time and I know housing managers are really worried that long-term residents and stable neighbourhoods will be forced to move on," he said.
"That could change the nature quite drastically of those kind of neighbourhoods so I think there's real concern about what this will mean in terms of neighbourhoods and community cohesion."
A Department of Work and Pensions spokesperson said: "It's only right that we bring fairness back to the system - when in Wales alone there are many thousands on housing waiting lists or living in overcrowded homes.
"We do not expect many people to have to move as a result of these changes and we are giving councils in Wales almost £6.2m to help vulnerable tenants with their housing needs."
A Welsh government spokesman said: "The Housing Minister Carl Sargeant has voiced his concern that the cut in housing benefit for tenants with spare bedrooms will have a devastating impact on many poorer households across Wales.
"Research shows that around 40,000 households in Wales will lose an average of £11 per week from this change and, sadly, it is many of the most vulnerable people in society who will be affected.
"The Welsh government is committed to doing all it can to ensure that the change does the least possible damage to our communities. However, we are under no illusion.
"We know that people will suffer hardship and this will put even more pressure on public services that are already straining to cope due to the current financial climate."