The Inland Revenue, responsible for implementing the minimum wage, is already receiving 3,000 anonymous calls a week about recalcitrant employers. And the Low Pay Unit has heard of several which are reducing workers' hours so that their wage bill does not go up.
Those most likely to benefit from the minimum wage will be women working part-time, according to the unit's latest statistics. Childcarers earn just pounds 2.83 an hour, while hairdressers, barmaids and waitresses get little more.
Many of the worst wages are to be found in the sweatshops of textile quarters, such as the East End of London. In one cramped factory last week, around 60 men and women - mostly Turkish and Kurdish - were hunched over lines of sewing machines and rows of ironing boards for 10- and sometimes 14-hour shifts. Retailers will buy the black, pin-stripe suits made there for pounds 6 each and resell them for pounds 60.
The atmosphere was hot. Clouds of steam from the presses filled the air and bars covered the blackened windows. It must be suffocating in the summer. It's hard to imagine working conditions could have changed since the beginning of the century.
The East End, originally because of its position near London's docks, has been a haven for immigrants and cheap labour, from the Huguenots of the 17th century to the Kurds of the early Nineties. In one corner of the factory a group of men played cards on low wooden benches while their boss was at lunch. They were shouting above the industrial hum of sewing machines. Ali, 24, is from Kurdistan and earns around pounds 2.50 an hour. His friend Kangir, who packs suits in plastic covers, earns pounds 2. "It really depends on your experience," he said. "If you're good you can earn pounds 8."
In his office, which is covered in posters of Helena Christensen, their boss, Cuneyt, shuffles through minimum-wage forms from the Inland Revenue. "We've got all the papers of course. I don't yet know how it will affect the people here. But we've got a bit of time yet."
The Government has stepped up its television, radio and press advertisements in several different languages, increasing its spending on the campaign from pounds 3m to pounds 5m. But are workers aware of the new law?
"Umm," said Cuneyt. "We've told them but 95 per cent don't speak English so you can't get much out of them. But yes, people are going to want more."
Cuneyt said he may be able to charge his retailers a higher price to cover the extra expense. But this seems unlikely considering retailers can dictate prices. "Factories like this won't even be here next year," he said. "Trade is dying on its feet. My father used to own a factory 50 years ago and workers were paid more than they are now."
Nearby, in Hackney's Kurdish community centre, earning a minimum wage seems about as likely as getting a company car or a pension. Clusters of men and women sit around, drinking coffee, smoking and waiting patiently for news of work.
"If you say something against an employer they'll sack you," said Meta, 28. "Some of them shout at you all the time and you have no right to defend yourself. Often you start at 7am and finish at 9pm."
Meta's main source of work is also in textiles. Because the sector is in decline, factory owners are less able than ever to pay their staff better wages. And the idea of challenging their bosses for more would be unthinkable for Meta and her friends.
"I've heard some awful stories," said Bhati Patel, director of the Low Pay Unit, citing a "cleaner whose employer cut her hours so he can raise her wage but still pay out the same money. Then there are care workers who have been told they'll receive extra training - which means they're exempt from the minimum wage."
How employees can confront this level of exploitation isn't made clear in the Government's ads. "The potential is there to deal with the worst cases," said Ms Patel. "But so is the potential for the employer to evade it. The employees will have to be the fighters. It's still up to them to challenge the employer and we're talking about a very vulnerable group of people."
Which is why Ali Aksoy, employment rights adviser for Swap (Service Workers Action Advisory Project), believes that the sweat-shop economy will carry on regardless. "They're scared of losing their jobs. If they take their employer to court, how long is that going to take? Months? In that time, he'll probably have lost his shifts anyway. The system is pushing people to pacifism. They don't complain and accept what they're given."
As one factory worker said, hunched over his trouser press: "I'm grateful to make what I can. I moved here from Turkey last year. It's very hard to find work but this is all I can do. Why would I risk asking for more? Who else would offer me work?" The Government's ads do not answer that.
TWO MILLION BETTER OFF
The minimum wage will affect 2 million workers in all. More than half of those benefiting - 1.3 million people - are women; 1.2 million are part-timers. Some 200,000 single parents should benefit, as will 200,000 younger workers above the age of 17. Eighty thousand low-paid homeworkers should also see their wages rise.
EXCEPT THE YOUNG,
16- to 17-year-olds are exempt from the minimum wage.
So are apprentices between 18 and 26 in the first year of their apprenticeships.
Trainees on government-funded training schemes are also exempt, as well as students on sandwich courses and teacher trainees.
... AND AU PAIRS
Those working and living in the family, such as au pairs, are exempt.
WHILE INFLATION BITES
The minimum wage may or may not be inflation-indexed. This depends on the findings of a Low Pay Commission report, to be completed at the end of the year.