The concession means new workers who sign a contract requiring them to work on Sundays can withdraw from Sunday working if they give their employers three months' notice.
The provision, inserted largely because of pressure from Christian Conservative MPs, was originally resisted by the Home Office on the ground that it would create a 'liars' charter', enabling prospective staff to say they would not mind working Sundays only to change their minds later.
However, the prospect of an alliance between Conservative and Labour MPs to insert an opt-out clause during the committee stages of the Sunday Trading Bill forced the Government to change its mind. Labour yesterday claimed this as an important climb-down for a Government bent on deregulation.
Peter Lloyd, the Home Office minister overseeing the Bill and an enthusiast for deregulation, acknowledged it was a 'small change in the direction of regulation' but said it was necessary to bring 'order, coherence and effective law' to the area.
The Government is to allow a free vote on Sunday trading which, after the second reading, will take place in a committee of the whole House of Commons. It hopes the three options to be debated - deregulation, restriction or partial deregulation - will be voted on in that order, although the eventual sequence will depend upon the Deputy Speaker, Michael Morris.
However, Mr Lloyd said that the Government will insist on a whipped vote against any proposal to make extra payment for Sunday working compulsory.
The three options MPs will vote on are lifting all restrictions on Sunday trading, the restrictive option supported by Keep Sunday Special and Retailers for Shops Act reform, a group led by Marks & Spencer, and the partial deregulation sought by the Shopping Hours Reform Council, which includes big stores such as Sainsbury and Tesco.
The restrictive option would allow most small shops, under 3,000 sq ft, to open, as well as garden centres, DIY and motor shops, but would limit large stores and supermarkets to the four Sundays before Chrsistmas. The partial deregulation proposal would allow big shops to open every Sunday for a maximum of six hours.
It is unlikely that total deregulation, privately favoured by most of the Cabinet, will win MPs' support and the big parliamentary battle is between the supporters of the other two