LONDON (Reuters) - Syrian refugee children have been working in factories in Turkey making clothes for British high street retailer Marks & Spencer and online store ASOS, an investigation by BBC Panorama has found.

The investigation, broadcast on Monday evening, found Syrian refugees as young as 15 working long hours for little pay, making and ironing clothes to be shipped off to Britain.

BBC journalists took photographs of Marks & Spencer labels in the factories. Some Syrian refugees worked 12-hour days in a factory distressing jeans for fashion brands Mango and Zara, using chemicals with inadequate protection, the BBC said.

An M&S spokesperson said: “We had previously found no evidence of Syrian workers employed in factories that supply us, so we were very disappointed by these findings, which are extremely serious and are unacceptable to M&S.”

M&S said it was working with the Turkish supplier to offer permanent legal employment to any Syrian daily workers employed in the factory.

“Mango has zero tolerance towards the practices described in the ‘Panorama’ program,” a Mango spokeswoman said.

The company said it had instructed an urgent and unannounced audit of the concerned facilities after the BBC’s notification. “Under no circumstances was the use of child labor of Syrian workers detected,” she said.

An ASOS spokeswoman on Monday said: “It’s a subject we take incredibly seriously. But it would be wrong for us to comment on reporting we haven’t seen.”

A spokeswoman from Inditex, which owns Zara, said the company had investigated Panorama’s report. “The factory BBC refers to - Goreteks - is a laundry that had already been audited by Inditex before Panorama’s filming took place. It is currently the subject of improvement measures,” she said.

The Inditex audit process was “a highly effective way of monitoring and improving conditions for workers,” she said. “We strongly reject any suggestion to the contrary.”

Turkey has been a main entry point for refugees from the conflict in Syria, with three million of them estimated to be living there. Ankara signed a deal with the European Union in March to stem the flow of refugees into the bloc.

A Reuters investigation this year also found evidence of Syrian refugee children in Turkey working in clothes factories in illegal conditions.