Discriminating consumers are used to boycotting wine from countries with dodgy human rights records or avoiding food produced by factory farms, writes Kathy Marks. But, so far, it hasn't occurred to many of us to find out how our clothes are produced. A new book entitled No Sweat aims to change all that by revealing that some of our favourite high-street stores sell clothes made in sweatshop conditions, and bringing consumer pressure to bear on the guilty producers. For example, did you know that many big- name trainers selling for pounds 80 are assembled for about 50 pence in Indonesia, or that pounds 50 jeans from Brompton Cross are sewn for about 25 pence?

By publishing No Sweat to coincide with London Fashion Week, radical publisher Verso hopes to highlight the fact that there is another side to the industry, far removed from the glitz and hype of the catwalk. This is a world of misery and exploitation, of child labour, cramped factories and starvation wages. The sweatshop is back in business and clothes sold in Europe and the US, including some of the most sought-after labels, are produced in conditions of Victorian squalor.

No Sweat's editor, American academic Andrew Ross, argues that the very structure of the clothing industry makes it difficult to police. Manufacturers farm out work to hundreds of competing sub-contractors who hunt around the globe for ever cheaper labour, often finding it in countries with dubious humanitarian records, such as China, Burma and Indonesia.

American groups have taken the lead in exposing the working practices of household-name companies. In 1995, Gap agreed to independent monitoring of its suppliers' factories after it was discovered that teenagers in El Salvador were working an 18-hour day for 28 pence an hour, sewing Gap clothes. Disney, which was using Haitian workers earning 18 pence an hour to sew Pocahontas T-shirts in rat-infested factories, recently agreed to issue a code of conduct to its suppliers. In Britain, charities such as Oxfam are trying to persuade the five main retailers - Burton, Next, Sears, C&A and Marks & Spencer - to agree a code of conduct. Fashion journalist Caryn Franklin has suggested that clothes should carry a label stating whether they were produced in humane conditions - one way of enabling us to exercise our power as consumers.

Sweatshops are not confined to the Developing World, says Ross. They are thriving in major western cities - London, Bradford, New York, Los Angeles - peopled by immigrants working long hours for subsistence wages. And, as Ross points out, most sweatshops supply the cheaper end of the market: "The people who can least afford to have a conscience about this are the ones who are most likely to buy sweatshop clothes," he says.

`No Sweat' is published by Verso (pounds 14) on 25 September.