Indian garment suppliers for large brands including Hugo Boss, Mothercare, Debenhams and Primark have been enforcing slave labour by holding female workers captive, an investigation has found.

German fashion brand Hugo Boss highlighted an instance of forced labour it had identified at a finished goods supplier in India in its 2016 sustainability report, where it said employees were prevented from leaving the company's premises at any time.

After the audit, the retailer said an action plan was defined in order to resolve the situation immediately, which it said it was monitoring "very closely."

An investigation by The Guardian investigation the report found that Best Corporation, located in Tamil Nadu and used by Hugo Boss, also supplies garments to high-street brands including Next and Mothercare.

One young woman who works at a the factory reportedly told the newspaper the women are not allowed to leave the premises without wardens or whenever they want to. Factory owners, however, say the policy is necessary to "ensure worker safety in largely rural areas."

The issue related to worker confinement is a widespread one in southern India, according to The Guardian, where young female migrant workers are housed in dormitories on factory premises. It is thought that more than half of the 743 spinning mills across the region were illegally restricting the free movement of resident workers, a survey by the India Committee of the Netherlands found.

The Guardian also found evidence of worker confinement at premises belonging to Sulochana cotton mills, which supplies Primark, and Sri Shanmugavel mills, which feed into Primark and Debenhams' supply chains.

According to multiple interviews with workers in factories belonging to Sri Shanmugavel mills, young women living at the factories are either not allowed mobile phones, or they have their calls monitored by factory supervisors.

A spokesperson for Primark said the connections to Primark in the report are either inaccurate or unfounded. It added: "We accept that we have a responsibility to improve employment conditions in the region and we have been working with other major UK and international brands, NGOs and worker rights organisations to do this.

"We are aware that the sector in this region has issues, which we are seeking to improve in accordance with the UN's Guiding Principles that encourage companies to work for improvement through collaboration, which is necessary given mills supply many brands. We have been a member of the ETI TNMS programme in the region since 2012, working to improve conditions in the spinning mills, including Sulochana Mills."

Hugo Boss, meanwhile, said it is committed to improving working conditions along its supply chain in collaboration with all relevant stakeholders, primarily its suppliers, but also with NGOs, policy makers, unions and other partners from the industry.

"We act in a responsible manner and take possible discrepancies in regards to our standards very seriously and we follow up on any issue with greatest care. Hence, we have actively reported about our findings at Best Corporation, who we are working with for body wear, in our 2016 Sustainability Report. Hugo Boss has since been in regular and intensive exchange with the company to jointly achieve improvements with regards to women's rights.

"To improve the situation in India in general, Hugo Boss is strongly committed to the Tamil Nadu Alliance Initiative of the Partnership for Sustainable Textiles in Germany (Bündnis für nachhaltige Textilien). The project is designed to work on improving labour standards in spinning mills and factories in the area together with local and international NGOs, Indian government officials and other textile companies. One of the measures is the implementation of extensive change management programmes in spinning mills, to raise awareness for sustainability issues in general and to foster the cooperation between the suppliers and external parties in this regard, as we consider this collaboration as crucial for success."

Debenhams and Mothercare did not return a request for comment at the time of going to press.