By Myles Neligan BBC News Online business reporter

More than three million people work in retail

Those who attempt to buy groceries on the traditional day of rest can expect thronged aisles and endless queues as millions of fellow consumers rush to stock up on household essentials to see them through the working week.

Britain's leading retailers say Sunday ranks as their second busiest day of the week, surpassed only by Saturday in terms of shopper numbers and sales.

But it's easy to forget that the Sunday supermarket stampede is a relatively recent phenomenon.

Until the 1994 Sunday Trading Act, which came into force 10 years ago this weekend, all but the smallest neighbourhood stores in England and Wales were legally obliged to close between Saturday evening and Monday morning.

The Act allowed big supermarket chains and department stores to open their doors for up to six hours on Sunday, fundamentally altering the texture of the weekend.

Sea change

Unsurprisingly, the move was roundly condemned by Christian pressure groups, who saw it as an affront to Britain's religious and cultural traditions.

Trade unions also voiced concerns that the change would impose added pressure on the retail workforce.

I find it difficult to imagine that there is anyone whose faith is so weak that they will go to the supermarket on Sunday instead of to church David Southwell, British Retail Consortium

But it was applauded by consumers, who welcomed it as a long-overdue attempt to accommodate their increasingly hectic and time-starved lifestyles.

It was also warmly welcomed by the supermarket groups themselves, who had long been pushing for a relaxation of the Sunday trading laws.

In fact, some stores had already been opening on Sunday in defiance of the law, secure in the knowledge that extra sales would amply exceed any fines the courts might impose on them.

Since 1994, the British retail sector has changed almost beyond recognition.

The major supermarkets have expanded far beyond their original role as simple food retailers, moving into clothes, medicines, petrol and even financial services.

Sainsbury, then the UK's biggest supermarket chain, has slipped into third place, caught on the hop by aggressive price competition from current leader Tesco and second-ranked Asda.

Safeway, formerly number four in the supermarket league, has disappeared altogether, snapped up last year by up-and-coming contender Morrison's.

And the sector has prospered thanks to a sustained consumer boom, with annual turnover soaring from £162.1bn ($291bn ; 243bn euros) in 1994 to a projected £262.2bn this year, according to retail consultants Verdict.

Revenue effect

Experts say Sunday trading has played no small part in this surge in revenues.

Sunday trading caters to busy lifestyles

"It certainly has boosted sales, although the precise effect is hard to quantify," says Nick Gladding, senior analyst at Verdict.

"Retailers will only open on Sunday if it's in their interests to do so."

The retail sector itself prefers to play down the sales impact of Sunday trading, saying its main effect has been to displace shopping that previously took place during the week.

According to David Southwell of the British Retail Consortium, the big supermarket chains only began campaigning for a relaxation of the Sunday trading laws when it became apparent that that was what their customers wanted.

"The old legislation reflected the cultural values and lifestyles of an earlier period. We are a very time-poor society, and the traditional housewife, who could do the shopping during the week, is a complete anachronism," he says.

Mr Southwell also has little time for the protestations of religious groups.

"I find it difficult to imagine that there is anyone whose faith is so weak that they will go to the supermarket on Sunday instead of to church."

Working hours

However, the retail sector's three million-strong workforce continues to have reservations about Sunday trading, and its objections are perhaps less easily dismissed.

Staff should be entitled to premium rates of pay on a Sunday Kevin Hegarty, USDAW

The big supermarkets initially overcame their employees' resistance by offering them higher rates of pay on Sundays, but some have since begun to erode the differential.

"We're concerned that the big retailers are trying to normalise working on Sunday, the one day that is collectively recognised as a day of rest," says Kevin Hegarty of shopworkers' union USDAW.

"Retail is a very busy sector and staff are under a hell of a lot of pressure. We believe that if they work on a Sunday, they should be entitled to premium rates of pay."

An Asda spokesman confirmed that the company's most recent employment contracts did not include extra pay for Sunday shifts.

Shopworkers are also concerned that having gained the right to open for six hours on a Sunday, the supermarkets now want more.

They point to a growing tendency by the big chains, including Asda, to throw their doors open half an hour earlier than strictly permitted on Sunday mornings in order to give their customers extra "browsing time."

Asda said it is not currently pushing for an extension of Sunday trading hours, but Verdict's Nick Gladding says there is little doubt that that is precisely what the major supermarket chains want.

"Sunday is one of the retailers' most important trading days, and they would like to make more out of it," he said.

There is every chance that in another ten years, the era of genuine 24/7 shopping will have arrived.