Britain's biggest retailer Tesco is to boycott the use of cotton from Uzbekistan in all of its clothing and textile products following allegations by campaign groups that child labour is used in harvesting the fibre.

In a letter to suppliers, Terry Green, CEO of Tesco Clothing, said: "The use of organised and forced child labour is completely unacceptable and leads us to conclude that whilst these practices persist in Uzbekistan then we cannot support the use of cotton from Uzbekistan in our textiles."

The supermarket chain is also calling on its suppliers to improve supply chain transparency by tracing the source of raw cotton used in all Tesco textile products from autumn/winter 08.

"We understand that cotton is an internationally traded commodity and that raw cotton sources are not always easily identifiable," Green said.

But he added that the retailer intends to "randomly audit records to monitor the source of raw cotton." If it is not possible to identify where the cotton has been grown, suppliers must alert the company before production begins.

A Tesco spokesperson was unable to tell just-style how much of the cotton used in its clothing and textile lines was sourced from Uzbekistan "because it's an internationally traded commodity and so lots of cotton from different sources gets mixed up."

But he added: "What we're doing now is that we've got a tracking system in place that will make sure our suppliers are aware of where they're sourcing their cotton from, and from that they'll be able to establish that it's not being sourced from Uzbekistan."

The Tesco ban comes after research carried out by The Environmental Justice Foundation (EJF) found that Uzbek cotton production uses state-sponsored child labour.

In its report 'White Gold: the true cost of cotton', the EJF claims that up to one-third of the Uzbek workforce is required to labour in the annual cotton harvest for very low wages.

This includes tens of thousands of children who are withdrawn from school to pick the cotton that funds President Karimov's government.

Uzbekistan is one of the world's biggest producers of cotton, with annual export revenues of around GBP500m (US$988m). Europe is a major buyer of Uzbek cotton.

Steve Trent, executive director of EJF applauds Tesco's decision and adds: "Tesco has proven that the sourcing of cotton fibre and the tracking of supply chains are entirely possible and there is no excuse for all other retailers of cotton goods not to pledge a commitment to do the same."