Sainsbury’s is to double the volume of Fairtrade cotton clothing it sells and increase its range as demand for ethical goods goes through the roof.

The grocer is to double its order of Fairtrade cotton to 640 tonnes for the financial year to March 2009, bringing the number of such garments it will offer to 3 million.

At present, the supermarket group sells 22 lines of Tu Fairtrade clothing, including t-shirts, jogging pants and jogging tops. A Sainsbury’s spokeswoman said the intention is to add further lines.

“That is the plan – that is why the order of cotton is going to double, so we can extend it into more lines and ranges,” she said.

In the year to the end of March, Sainsbury’s is on track to sell about 2 million Fairtrade t-shirts – its best-selling line of Fairtrade clothing. This represents a dramatic increase on the previous year.

Some of the UK’s top retailers have invested heavily in Fairtrade clothing, as ethical concerns shoot up the retail agenda. Tesco is poised to unveil a Fairtrade denim range just after Fairtrade Fortnight, which has been running from February 25 to March 9.

This year, Tesco is likely to become the world’s second-biggest retailer of Fairtrade cotton – behind Marks & Spencer – by selling between 15 million and 20 million men’s, women’s and children’s garments.

During Fairtrade Fortnight, M&S introduced Fairtrade-certified cotton to its Limited Collection.

Last month, Debenhams launched its Fairtrade menswear range with Sir Steve Redgrave. Maine New England, one of Debenhams’ brands, has teamed up with the Olympic champion’s clothing range FiveG to produce an exclusive menswear collection made from Fairtrade-certified cotton from Mali.