Bangladeshis making cheap clothes for Asda, Tesco and Primark are paid as little as 3p an hour, according to a report that claims to reveal the grim truth about Asia's sweatshops.
Basic pay in factories that cut and sew fabric for budget chains could be just £8 a month for an 80-hour week, investigation for the charity War on Want found.
Overtime payments of around £3 a month meant some workers were receiving just £11 a month for a seven-day week - 3.1p an hour. On top of that, workers complained that joining a trade union was banned and bosses cheated them of overtime pay. Beatings and sexual harassment were also said to occur.
According to the report, 22 union members at a factory supplying Asda who demanded overtime pay last year were allegedly beaten, fired and imprisoned on false charges. They claimed they had been required to do 19-hour shifts and paid no overtime.
War on Want interviewed 60 workers from six factories for its report, Fashion Victims, published on the day of the annual meeting of Associated British Foods, which is expected to report booming profits at Primark.
The charity chose the six factories at random to highlight conditions at suppliers for the budget end of British fashion. All six supplied Asda, four Tesco and three Primark.
Researchers gained the trust of the workers before interviewing them after 8pm at home when they had finished their shifts. Many had begun work at 7am. A living wage was estimated to be £22 a month in Bangladesh. Yet workers said the starting wage at the six factories ranged between £7.54 and £8.33 a month. Sewing-machine operators were paid more - £16 a month, about 5p an hour. The Bangladeshi minimum wage has remained at £7 a month since 1994 but may soon rise to £12.
Asda, Tesco and Primark are members of the Ethical Trade Initiative, whose code of conduct imposes a 48-hour week for workers and stipulates they should have one day off. Overtime shall be voluntary and not exceed 12 hours a week.
The report said: "Investigation for this report shows that, in reality, working hours in factories supplying all three retailers far exceed this maximum.
"Across all six factories, most workers told us that they work from 12 to 16 hours per day and regularly work 80 hours a week."
Officially, Friday was the day off but staff said that most weeks they were required to work for seven days. One worker, Abdul (not his real name), said: "If someone is absent on Friday then they would be verbally abused or their six to eight hours overtime wage would be deducted as punishment."
Workers complained they were routinely defrauded of overtime payments and there was a pervasive air of deprivation.
Decades of under-investment and worsening wages and working conditions in Bangladesh - which has the cheapest garment workforce in the world - "spilled over" during 2006, according to the report.
In February and March a spate of garment factory collapses and fires left almost 100 workers dead and many more injured. Yet workers claimed that emergency exits in their workplaces were often kept locked.
In 2005, hundreds of workers in a Bangladeshi factory reportedly producing for Primark were fired in a conflict with the management when a superviser physically assaulted three workers, allegedly for making mistakes.
The report said factories passed audits by the Western retailers by intimidating staff to lie. Many auditors gave factories 20 days' notice, plenty of time to clean dormitories, coach the workers and falsify records. The report said: "Retailers like Asda and Tesco often point to the audits they use to check working conditions. But these kind of bulk auditing systems provide only a superficial assessment."
Dr Liu Kaiman, of the Institute of Contemporary Observation in Shenzhen, China, was quoted as saying: "The retailers and their suppliers are playing an elaborate game. They only want to reassure customers, not to improve conditions."
The thriving value-clothes market in the UK is worth £7.8bn, with Asda the biggest player with 17 per cent, Primark second with 15 per cent and Tesco fourth after Matalan with 11 per cent.
Primark said that if War on Want provided details of the factories, it would investigate. "Our low prices are the result of technology, efficient distribution and supply, bulk-buying and the fact that we spend almost nothing on advertising," said a spokesman.
Tesco stated that its affordable clothing was not achieved through poor working conditions at suppliers.
Asda said only organisations like War on Want and the retailers were trying to help workers and promised to introduce more unannounced audits and free phone lines for whistleblowers.
Lina Begum, 22: Forced to work 14-hour days
Work starts for Lina at 8am, sewing clothes for Primark, Tesco and George at Asda. She usually finishes work at 7pm but sometimes works on between 8pm and 10pm.
One of eight children, Lina (not her real name) puts up with the shifts because she wants to help her family in the countryside. Her father is a labourer and subsistence farmer. When Lina was 12, a brother contracted typhoid and went blind because of a wrong treatment.
During his illness Lina and her mother travelled to Dhaka for help. To fund the treatment, the family had to sell land and borrow money. Poverty meant the family had only one meal a day and could no longer afford Lina's school costs.
During her trip to Dhaka, she heard about the garment factory and got a job there in 1997, aged 13. In 2004 she married a colleague in the same factory. After her marriage, she could not send money to her parents regularly because living costs had risen. In November 2005, her husband fell ill. She cannot send money to her parents regularly because she has to pay for her husband's treatment.