Sunday trading laws will be suspended during the London 2012 Olympics in a bid to cash in on the Games, Chancellor George Osborne is expected to announce in the Budget.
Emergency legislation will be used to lift the six-hour limit on the opening hours for larger stores across the whole of England and Wales on eight weekends covering the Olympics and Paralympics.
Officials hope hundreds of thousands of visitors flooding to the capital for the sporting spectacle will take advantage of late-night shopping in the West End, boosting flagging retail figures.
But the move is bound to meet stiff opposition from church leaders and some Tory backbenchers who have already warned that it was likely to lead to a permanent relaxation. And Labour accused the Chancellor of a "disgraceful breach of the need for a proper consultation and negotiation with trade unions and other groups".
Under the Sunday Trading Act 1994, large shops over 280 square metres in England and Wales are restricted to six hours' continuous trading between 10am and 6pm on Sundays and cannot open at all on Easter Sunday.
Without a change in the law, that would also mean the three biggest souvenir shops at the Olympic village itself in Stratford, east London, would have been forced to close their doors to spectators. Details of the plans emerged as Mr Osborne said in the Budget he wanted "to ensure it is the working person who gets most support".
There was also a need for "major reforms to our planning laws" to encourage foreign investment and create jobs, he told The Sun Sunday. He is due to meet Prime Minister David Cameron, Deputy Prime Minister Nick Clegg and Treasury Chief Secretary Danny Alexander - the so-called "Quad" - to iron out the final details.
The Budget "scorecard" has already been presented to the Office for Budget Responsibility so it can calculate the economic impact of the proposed changes in time for the set-piece.
It was widely reported at the weekend that Mr Osborne was set to reduce the 50p top rate of income tax - which senior Liberal Democrats have said they would back in return for other measures to target wealth. But a poll found most voters were against a tax cut for £150,000-plus salaries - including half of Tory supporters, with Liberal Democrats the most hostile to the change.
And Mr Osborne also came under a barrage of angry criticism from trade unions over plans to push ahead with reductions in public sector salaries in some poorer parts of the country.