The Sunday Trading Act, which was passed earlier this year, takes effect today, permitting large shops to open for six hours on Sundays and small ones to open for as long as they like.
But many supermarket and garden centre customers will notice little difference, as their favourite haunts have been doing business illegally for more than a year.
Indeed some, if they are to end their defiance of the law, will find their hours shortened under the new Act.
The most noticeable change will be the opening of the big shopping centres such as Lakeside Thurrock and the Gateshead Metro Centre, with their 'high street' array of retail names.
However, in the real high streets, the picture is expected to be more patchy.
Those two flagships of upmarket shopping, London's Harrods and Selfridges, are not deigning to admit the public today.
John Lewis, the department store chain owned by its employees, has decided to maintain its traditional stance and stay closed on Sundays, although some of the group's Waitrose supermarkets will open.
Waitrose is widely seen as one of the weaker supermarket contenders, which cannot therefore afford to remain aloof from what is expected to be a tough battleground on Sundays.
The other big group to hold out against Sunday trading until today is Marks and Spencer.
Ten M&S stores will be open in England and Wales tomorrow.
'It's impossible to say what trade will be like. We have our own estimates but really we'll just have to wait and see,' said an M&S spokeswoman.
'We'll be doing nothing different at those stores that are open. We've had no problem getting staff to volunteer for work.'
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