The cost of living has been rising more quickly for poor households as a result of higher energy and food bills.
The TUC said CPI inflation for the poorest 10th of households in February was 4.1 per cent, compared to 3.3 per cent for the richest 10 per cent.
Poorer families were hit by higher inflation last year because they spend more of their income on food and utilities, said the TUC.
General secretary Brendan Barber said: “People have been getting poorer every month for the last two years as high inflation, tax rises and the dire state of the economy take their toll on family budgets.
“Over the last year the poorest households have suffered more than anyone else from rising food prices and soaring gas and electricity bills. The Chancellor’s obsession with raising VAT, along with swingeing cuts to tax credits, has made life even tougher for those on low to medium incomes.”