The document, from the Left Economics Advisory Panel, found that prices on essential items like food, water, electricity and council tax were rising faster than the official inflation rate.

Because low-income households spend more of their money on essentials than the wealthy, this meant an effective inflation rate of 1.92% for the poorest tenth of society at a time when prices were falling for the richest, it found.

As a result, the pay freezes imposed by many companies and public sector bodies in response to the recession meant a drop in living standards for the poorest workers, but amounted to a real-terms increase for the rich.

Report author Andrew Fisher said unions were “correct to argue that low-paid workers should not be treated the same in pay negotiations as senior management grades”.

Unions representing the lowest-income workers need to demand rises of at least 2% simply to maintain living standards, he said.

The report was commissioned by the Trade Union Co-ordinating Group, which welcomed its recommendation for the introduction of a new measure of “Essential Inflation” alongside the Retail Price Index and the Government’s preferred Consumer Price Index.

Bob Crow, general secretary of the RMT transport workers’ union, said: “It is clear from this important piece of research that the working class have taken by far and away the biggest hit in this recession.

“While pundits talk about falls in inflation, out there in the real world it’s a day to day struggle for people to make ends meet as the cost of essentials continues to rise.”

TUCG parliamentary convenor John McDonnell added: “This evidence will now shape trade unions’ strategy in coming pay negotiations. Trade unions cannot be expected to stand back and allow the living standards of their members to be eroded when they’ve witnessed the return of the bankers’ bonus culture.”

The report found that essentials - housing, utility bills, food and drink, clothing and transport - cost the poorest households more than two-thirds of their expenditure, compared to less than one-third for the richest. Even when they are feeling the pinch, poor people are unable to do without these items or even cut back significantly on them.

Wealthy households’ spending on mortgages has tumbled during the recession as the Bank of England slashed interest rates, while the rents paid by most poor households have risen.

Because of these differences, the report calculated the Essential Inflation rate for the poorest tenth of society at 1.92% in February this year, compared to -3.21% for the richest tenth. At the time, RPI inflation stood at zero, while the CPI rate was 3.2%.

Mr Fisher urged the Government to ask the Low Pay Commission to reconsider its recommendation of a 1.1% increase in the National Minimum Wage next month, arguing that this would amount to a decline in the living standards of low-paid workers.