Before tax credits, there was something called Family Income Supplement for working families and Supplementary Benefit for non-working families, help with rent via HB and its forerunner, rent rebate, and a rebate on "rates," which was what we had before poll tax and council tax.
Going back even earlier, there was National Assistance, introduced by the Attlee government in 1947 or '48.
Something like 40% of people on UC are working. Many claims are purely for help with housing costs, because we live in an age where there are no controls on private sector rents and they are unaffordable for families on low or even average incomes. And childcare is horrendously expensive for the youngest children.
When the average rent on a family home is more than the average take-home pay in many parts of the country, people need financial support to keep a roof over their heads.
I work in welfare rights, so know the breakdown of a lot of clients' UC payments. Housing is nearly always the biggest element. I'd love to know what proportion of the "benefit bill" goes to landlords. I'm convinced that more social housing would reduce costs in the medium term, and I know it would reduce them in the long term. As would rent controls.
Of course, benefit bashers never moan about the amount of money that pays the BTL mortgages of landlords. The housing system is fucked.