Nearly half a million UK families are thought to have fallen behind on rent, as a result of the coronavirus crisis, according to the Resolution Foundation.
It said more than 750,000 had been behind on housing costs last month.
That is 450,000 more than January 2020.
While 1 in 20 private renters in the UK said they had been refused rent reductions.
Many had taken “huge hits” to their earnings and had “limited savings” to fall back on, research director Lindsay Judge said.
“To make matters worse, measures that could ease the pressure, such as discretionary housing payments from local authorities and negotiated rent reductions from landlords, are not getting through to those that need them.”
Almost 1 in 4 private renters had seen their income fall as a result of the crisis, the body said.
And it did not expect an easing of lockdown restrictions to be enough to solve their problems.
“Both benefit cuts and the end of furlough are pencilled in for the spring, either of which will strain family incomes further,” it said.
“Likewise, unemployment looks set to rise, rather than fall, through 2021, potentially driving up arrears further still.”
Landlords in England have been banned from evicting tenants until at least the end of March, offering “some security”, the Resolution Foundation said, by preventing families under the most strain becoming homeless during the pandemic.