Better off families are more than three times as likely to have become richer since the coronavirus lockdown hit than poorer ones, the Resolution Foundation has found.
High-income families are also far, far less likely to have struggled with bills since lockdown forced businesses to close, it added.
Separate research from Stepchange Debt Charity also found people with an income of less than Sh4 million (£30,000) are particularly likely to have fallen behind or borrowed to make ends meet during the crisis.
Resolution Foundation research director Laura Gardiner said: "Many high-income families have reduced their spending in recent months.
"Those on lower incomes, however, have found it far harder to reduce spending which, when combined with income falls, means many are seeing their ability to manage financially deteriorate."
While 38 per cent of richer families managed to strengthen their bank balances during lockdown - just 12 per cent of worse off ones did.
Poorer households are also much more likely to say that their ability to manage financially has worsened than improved (37 per cent compared with 10 per cent).
More than half (57 per cent) of the richest fifth of families have been able to reduce their spending since the crisis began, including one in 10 (10 per cent) who have cut their spending by more a quarter, the report found.
By contrast, less than a third (30 per cent) of the poorest fifth of households have managed to cut their spending.
People in the low income bracket are nearly as likely to have increased their spending during the crisis (27 per cent) as they are to have reduced it, the Foundation said.
Those in the top fifth meanwhile are about as likely to say their position has improved as they are that it has worsened (23 per cent compared with 22 per cent).
The findings were released as a separate report, from StepChange Debt Charity, warned that a "personal debt tsunami" of around £6 billion of additional household debt directly attributable to the coronavirus pandemic is being stored up.
Based on survey findings, StepChange estimates that 4.6 million people negatively affected have already accumulated £6.1 billion of arrears and debt.
The charity said that while temporary measures are in place to give relief to borrowers, longer-term measures are needed to protect struggling households against unaffordable repayment demands.
StepChange chief executive Phil Andrew said: "We were already dealing with a debt crisis, but Covid has so far added another four million people and counting to the number who are going to need help finding their way back to financial health.
"With Sh806 billion (£6 billion) of additional household debt directly attributable to the effects of the pandemic, this is a problem that isn't going to solve itself."
Iain Porter, policy and partnerships manager at the Joseph Rowntree Foundation, said: "Rising costs and increased bills, combined with disruption to food banks and advice teams, mean some families are really struggling to keep their heads above water."