Revenue: 'Earn until May' to cover your tax bill

The Adam Smith Institute predicted that "tax freedom day" would fall on May 30 2011, meaning the equivalent of every penny earned by the average worker for the first 149 days of the year will go to the Treasury.

It said the longer period – six days more than in 2009 – was almost entirely down to the extra revenues the Government expects to rake in by increasing the sales tax from 17.5 per cent to 20 per cent from January 4.

If the calculations prove accurate, it will be the latest the milestone has fallen since 2007 when it stretched into June.

Tom Clougherty, the Institute's executive director, said: "The Government is right to give priority to cutting spending and plugging the deficit. But as Tax Freedom Day shows, Britons are still desperately overtaxed.

"The fact that we spend almost five months working for the state and only seven months working for ourselves and our families is a shocking indictment of big, wasteful government.

"As well as hitting every household in the country, the VAT hike is going to dent consumer confidence and put a dampener on our economic recovery – as the Office of Budget Responsibility has already pointed out."

Dr Eamonn Butler, director of the Institute, said: "The coalition should examine the possibility of making targeted tax cuts now to encourage economic growth.

"But in the long term, they need to fundamentally overhaul the entire tax system. Lower, simpler, flatter taxes would be fairer for individuals, and better for the economy."

Chancellor George Osborne earlier this month tried to dampen expectations of tax cuts ahead of the General Election scheduled for 2015.