https://www.gov.uk/government/publications/number-of-housing-benefit-claimants-and-average-weekly-spare-room-subsidy-amount-withdrawal

16.6 per cent of housing benefit claimants in the social sector were affected by the under occupancy rules in February 2014 (DWP statistics).

477,601 claimants were affected with an average reduction of £14.32 per week.