The latest undercover BBC investigation has found Syrian refugee children have been making clothes for British shoppers.
Panorama investigated factories in Turkey and found children had been working on clothes for Marks and Spencer and the online retailer Asos. Refugees were also found working illegally on Zara and Mango jeans.
All the brands say they carefully monitor their supply chains and do not tolerate the exploitation of refugees or children.
Marks and Spencer says its inspections have not found a single Syrian refugee working in its supply chain in Turkey, while Panorama found seven Syrians workers. They were employed through a middleman who paid them in cash on the street and offered little more than a pound an hour - well below the Turkish minimum wage.
The youngest worker was 15 years old and he was working more than 12 hours a day ironing clothes before they were shipped to the UK.
A spokesperson for Marks and Spencer said the programme's findings were "extremely serious"
and "unacceptable to M&S"
. It is offering permanent legal employment to any Syrians who were employed in the factory.
Also Syrian children were found doing hard work in one back-street workshop in Istanbul. Asos accepts its clothes were made in the factory, but says it is not an approved factory. The company has since inspected and found 11 Syrian adults and three Syrian children under 16 at work.
Asos says the children will be financially supported so they can return to school and the adult refugees will be paid a wage until they have been found legal work.
The investigation also found Syrian refugees working 12-hour days in a factory that was distressing jeans for Mango and Zara. The refugees were involved in spraying hazardous chemicals to bleach the jeans, but most of the workers did not even have a basic face mask.
Mango says that the factory was working as a sub-contractor without its knowledge. Its subsequent inspection did not find any Syrian workers and found "good conditions except for some personal safety measures".
Zara's parent company, Inditex, says its factory inspections are a "highly effective way of monitoring and improving conditions".
It had already found significant non-compliance in an audit in June and had given the factory until December to make the necessary improvements.
Most of the refugees do not have work permits and many of them are working illegally in the garment industry."They speak of pitiful wages and terrible working conditions. They know they are being exploited but they know they can do nothing about it,"
Panorama reporter said after talking with dozens of Syrian workers.
Critics also say the retailers are not doing enough to stop the problems highlighted by Panorama. Danielle McMullan, from the Business & Human Rights Resource Centre, says the brands need to understand that they are responsible."They have a responsibility to monitor and to understand where their clothes are being made and what conditions they are being made in,"