The lack of progress comes as Tesco faces pressure from activist shareholders over the issue of ethical supply chains.

Retired solicitor Ben Birnberg, company secretary of War on Want, is campaigning to force Tesco to put a resolution on the agenda of the retail giant's AGM next month.

In a telephone interview, Bangladeshbased researcher Khorshed Alam told the Sunday Tribune that the only major change in conditions was that some factory owners were now paying their staff the new national minimum wage of 17 a month.

This remains, however, 15 a month below Bangladesh's minimum living wage, which is estimated to be around 32 a month.

Alam also said that at least 60% of factories had yet to adopt the new wage, despite a government demand that they implement it by the end of next month.

"Apart from that, there's not been much change in terms of the suppliers' behaviour towards their workers. They still work at night, they still work long hours, they still have to do forced overtime and their hours still aren't calculated properly."

He said Penneys and Tesco had the power to force suppliers to improve working conditions if they wanted to.

"They have a responsibility to put pressure on their suppliers and they must look into their supply chain."

A spokesman for Penneys said it was "a little bit in the dark about the precise allegations" and claimed that War on Want had not supplied it with information it had sought about the factories it identified in its report.

He said, however, that since the report was published, it had carried out audits of all the factories it used in Bangladesh and it had found a number of "minor infringements".

He admitted that one of the main reasons Penneys was able to sell clothes cheaply was because it used Asian factories.

"It's true. We operate in low-wage economies and it's true of a lot of other sectors where clothes come from China and the Far East, " he said.

Tesco said in a statement that "we are constantly checking and monitoring our supply chain including independent audits. Our suppliers comply with local labour laws, and workers at all Bangladeshi suppliers to Tesco are paid above the national minimum wage".

The supermarket is currently battling attempts by War on Want's Birnberg to force it to appoint an independent auditor to assess its trading ethics. Birnberg hopes to secure shareholders' support for his proposal at the company's annual general meeting next month.