A women's rights charity behind a T-shirt campaign caught up in controversy over claims the products were made in sweatshop conditions has said it will withdraw the garments if the reports are correct.

The T-shirts, worn by Ed Miliband, Nick Clegg and Harriet Harman proclaiming their feminist credentials, are made by women paid 62p an hour, it was reported.

A Sunday newspaper said its investigation had found the shirts, displaying the words, "This is what a ­feminist looks like", were produced in a factory on the Indian Ocean island of Mauritius where the machinists sleep 16 to a room. Fashion retailer Whistles, which sells the garments for £45, described the allegations as "extremely serious" and said they would be investigated.

The T-shirts made the news last week when Mr Miliband and Mr Clegg posed in them for Elle magazine in a campaign by the Fawcett Society - which receives the profits - to promote women's rights. After David Cameron refused to join them, Ms Harman, the Labour deputy leader, wore one at Prime Minister's Questions in an attempt to embarrass him.

Dr Eva Neitzert, deputy chief executive at the Fawcett Society, said the charity had been assured the shirts were produced to "ethical standards" by Whistles.

She said it had originally been told the garments would be produced in the UK, but samples received in early October showed they were made in Mauritius.

A spokesman for Whistles said: "The allegations regarding the production of T-shirts in Mauritius are extremely serious and we are investigating them as a matter of urgency."