The council tax system has been described as flawed by experts, particularly as council tax rates in England and Scotland are based on the value of properties in 1991.
The Resolution Foundation said the poorest fifth of households across the UK paid 4.8% of their income on council tax in 2020-21, up from 2.9% in 2002-3.
It comes as new analysis found the poorest households are paying an increasing proportion of their income on council tax.
Councils with responsibility for delivering social care can increase the tax by up to 4.99% - the threshold that would trigger a local referendum in normal circumstances.
Lalitha Try, an economist at the Resolution Foundation, said: “This terribly designed tax increasingly resembles the very thing it was meant to replace - the dreaded poll tax.”.
