It would probably just prompt consumers to alter when they shop, rather than how much they buy
Some hard-headed economic calculations lie behind an emotive row over whether or not supermarkets should be made to close early on Sundays. In public, the argument over Sunday trading goes back and forth over ground that we can all understand and on which we can hold opinions – such as whether a customer's right to shop when and where he or she chooses matters more than religious or social objections that it is restful to have one day in the week when the frantic pace of commerce slows and people – including staff who work in supermarkets – can spend time with their families.
As you would expect, the churches and the shop workers' union, Usdaw, are prominent advocates of keeping Sunday special, while the supermarket chain Asda is a powerful voice in favour of customer choice.
What might come as more of a surprise is that there are prominent people in the retail trade who do not want Sunday trading restrictions to be abolished. They include Justin King, the chief executive of Sainsbury's, who has warned that "a great British compromise is in danger of being lost".
Sunday trading will be one of the first issues in David Cameron's in-tray when he returns from his holiday in Majorca this Thursday. It is a political hot potato that could cause yet more trouble between the Conservatives, who favour unrestricted Sunday trading, and their Liberal Democrat partners, who oppose it.
The Prime Minister is likely to be fairly neutral on emotional questions about whether Sunday is a special day, and to focus on the economics. The Communities Secretary, Eric Pickles, has hinted that he is receptive to the argument that longer supermarket opening hours means more cash in the tills. The question is whether the supposed extra trade will be worth the social costs – and that cannot be answered, because no one has any reliable data.
Before restrictions were temporarily lifted for the Olympics, the law restricted the major shops in England and Wales to six hours' trade on a Sunday, which most interpreted as meaning from 10am to 4 pm or 11am to 5pm. Shops with a floor space of less than 3,000 sq ft can stay open longer. Since the relaxation came into force on 22 July, five Asda stores near the Olympic Park have been open 24 hours on a Sunday.
Asda's other London stores have stayed open until 10pm, stores outside the capital until 8pm. Asda has been giving ministers "regular feedback" on what the customers think of this change, which they say has "become more popular as time moved on". But they cannot translate that into hard figures. An Asda spokesman said it is "too early" to put a figure on how much extra business has been generated.
"Our customers like the convenience of us being open longer, as it means they can shop when it suits them, not when it suits us," he said.
The Labour Party is focused on the potential impact on the family lives of supermarket staff. "Sunday is a day which families can spend together and this should not be threatened by supermarket shop workers being pressured into working longer hours," said shadow planning minister, Roberta Blackman-Wood. "Longer hours for customers would also create longer working Sundays for their staff."
But just as the shops cannot say how much extra business Sunday trading has generated, the unions cannot offer anything more than "anecdotal evidence" that supermarket staff have been coerced into Sunday working.
The economic benefits do remain uncertain. Victoria Redwood, the chief UK economist at Capital Economics, believes that the overall impact of permanently extended Sunday trading "might not be very large". She said: "It would probably just prompt consumers to alter when they shop, rather than how much they buy. Larger retailers, including department stores and supermarkets, would stand to gain most, as they are currently most affected by the restrictions. Small independent stores would lose out."