Paul Johnson, director of the Institute for Fiscal Studies, asks why Britain spends such vast sums on Housing Benefit - now £25 billion. He examines the history of these payments and how government funding for house-building has gradually changed into subsidies for rents, especially to private landlords. 40% of tenants in private housing receive Housing Benefit. Critics argue that these have distorted the market and failed to address the fundamental shortage of housing supply. Paul asks how we got here and whether anything can change.

Producer: Adam Bowen.