Families living in council or housing association accommodation whose property is deemed to be larger than they need will receive less housing benefit from the beginning of April.
Those with one spare bedroom will lose 14% of their housing benefit, while those with two or more spare bedrooms will lose 25%.
The new rules allow one bedroom for each adult or couple. Up to two children under the age of 16 are expected to share, if they are the same gender. Those under 10 are expected to share whatever their gender.
Termed the single room subsidy by ministers, or the “bedroom tax” by Labour, the changes will result in £490m savings for the taxpayer in 2013-14.
The government estimates that more than 660,000 claimants will be affected, with an average loss of £14 per week. Families with severely disabled children, foster carers and families of armed services personnel will be exempt.
Couples with no children and older people – those most likely to have spare rooms – will be particularly hit by the changes. The changes will also affect different areas of the country to a lesser or greater degree.