Since April, people deemed to have one spare bedroom have had their housing benefit reduced by 14%, while those with two or more spare bedrooms had reductions of 25%.
One in five Citizens Advice clients in housing arrears were stung by the under-occupancy penalty.
In a statement, the National Housing Federation said: “Years of failed housing policy mean our stock of affordable housing is woefully inadequate and for most people affected by changes to Housing Benefit, moving to a smaller home is just impossible.
“Changes like the under-occupancy penalty are pushing some families over the edge into debt and at risk of losing their home.”
"Getting the cost of Housing Benefit down cannot be done safely without addressing the supply of homes. Increasing costs for a small number of families without radically improving our housing stock is an upside-down approach which does nothing to tackle the root cause of our country's housing crisis."
