Marks & Spencer has been accused of failing to pay Asian workers making its clothes sufficiently, six years after supporting a living wage.

M&S launched its Plan A environmental and social policy in 2010, under which it pledged to “implement a process to ensure our suppliers are able to pay workers a fair living wage” in India, Bangladesh and Sri Lanka.

M&S said it achieved that target last year after making a “significant difference” to working conditions in its clothing supply chain.

However, a new report by the workers’ rights group Labour Behind the Label has claimed that staff working in three factories in India, the same number in Sri Lanka and a further two in Bangladesh were still being paid less than a living wage.

In India, workers were earning an average of 6,284 rupees (£64) per month, according to the report, but said they needed more than double that amount in order to have a decent standard of living. Employees from the country who were interviewed for the report said food and education expenses were difficult to meet on their wages.

Pay in Sri Lanka averaged 13,500 Sri Lankan rupees (£64) a month, but the report suggested workers required as much as 33,000 (£158).

Researchers only spoke to a small number of workers in Bangladesh, but said they were earning a maximum of 8,000 taka (£70) per month when 15,000 taka (£131) would constitute what they considered to be a living wage.

Labour Behind the Label campaigner Anna McMullen told the Guardian she was “disappointed and angry” that M&S had not made a difference to the lives of its workers in Asia and called on the retailer to be more transparent about its supply chain so that conditions could be improved.

M&S said the price it paid suppliers was now sufficient for them to pay a living wage to staff in the three Asian countries.

The retailer added that more than 750,000 workers across the three countries have been trained in financial literacy, healthcare and workers’ rights since 2010.

An M&S spokeswoman said: “We are committed to further improving working conditions in our clothing supply chain and our work since 2010 has made a significant difference. For example, average wages at our supplier factories in Bangladesh are now 60% above the current minimum wage.

“There’s always more to be done due to the complex nature of the clothing supply chain and we cannot determine the wages paid to supplier employees.

“However, we are committed to ensuring our cost prices remain high enough to pay a fair living wage, training workers in financial literacy and worker rights, and playing our part in collaborating with other brands and governments to improve the sector.”