One in four housing benefit claimants in Copeland, Cumbria, has had their support cut thanks to the "bedroom tax" - the highest proportion anywhere in Britain.
Some 1,235 residents out of just under 5,000 have seen their benefit reduced by around £15 a week, new figures from the Department for Work and Pensions show.
The bedroom tax - officially known as the spare room subsidy - was introduced by the Conservative-Liberal Democrat coalition government in 2013.
It removes up to a quarter of housing benefit from working-age people renting from councils or housing associations, if they are deemed to have more bedrooms than they need.
Copeland's figure of one in four claimants affected by the tax, or 25%, compares with a national average of just 9%.
The next hardest hit areas, by local authority, are East Ayrshire (23%), Falkirk (22%) and West Dunbartonshire (21%).
Blackpool has the lowest proportion - just 2.6%, or around one in 38 claimants.
The figures, for August 2015, also show that a total of 4.79 million people in Britain currently claim housing benefit, and receive an average of £95.30 a week.
Almost a quarter of all claimants (23%) are in work - the highest number since comparable records began, and more than double the figure six years ago (11%).
Just over two-thirds of claimants rent some form of social housing.