Child workers, some as young as 10, have been found working in a textile factory in conditions close to slavery to produce clothes that appear destined for Gap Kids, one of the most successful arms of the high street giant.

Speaking to The Observer, the children described long hours of unwaged work, as well as threats and beatings.

Gap said it was unaware that clothing intended for the Christmas market had been improperly subcontracted to a sweatshop using child labour. It announced it had withdrawn the garments involved while it investigated breaches of the ethical code imposed by it three years ago.

The discovery of the children working in filthy conditions in the Shahpur Jat area of Delhi has renewed concerns about the outsourcing by large retail chains of their garment production to India, recognised by the United Nations as the world's capital for child labour.

According to one estimate, more than 20 per cent of India's economy is dependent on children, the equivalent of 55 million youngsters under 14.

The Observer discovered the children in a filthy sweatshop working on piles of beaded children's blouses marked with serial numbers that Gap admitted corresponded with its own inventory. The company has pledged to convene a meeting of its Indian suppliers as well as withdrawing tens of thousands of the embroidered girl's blouses from the market, before they reach the stores. The hand-stitched tops, which would have been sold for about £20, were destined for shelves in America and Europe in the next seven days in time to be sold to Christmas shoppers.

With endorsements from celebrities including Madonna, Lenny Kravitz and Sex and the City star Sarah Jessica Parker, Gap has become one of the most successful and iconic brands in fashion. Last year the firm embarked on a huge poster and TV campaign surrounding Product Red, a charitable trust for Africa founded by the U2 lead singer Bono.

Despite its charitable activities, Gap has been criticised for outsourcing large contracts to the developing world. In 2004, when it launched its social audit, it admitted that forced labour, child labour, wages below the minimum wage, physical punishment and coercion were among abuses it had found at some factories producing garments for it. It added that it had terminated contracts with 136 suppliers as a consequence.

In the past year Gap has severed contracts with a further 23 suppliers for workplace abuses.

Gap said in a statement from its headquarters in San Francisco: 'We firmly believe that under no circumstances is it acceptable for children to produce or work on garments. These allegations are deeply upsetting and we take this situation very seriously. All of our suppliers and their subcontractors are required to guarantee that they will not use child labour to produce garments. In this situation, it's clear one of our vendors violated this agreement and a full investigation is under way.'

Professor Sheotaj Singh, co-founder of the DSV, or Dayanand Shilpa Vidyalaya, a Delhi-based rehabilitation centre and school for rescued child workers, said he believed that as long as cut-price embroidered goods were sold in stores across Britain, America, continental Europe and elsewhere in the West, there would be a problem with unscrupulous subcontractors using children.

'It is obvious what the attraction is here for Western conglomerates,' he told The Observer. 'The key thing India has to offer the global economy is some of the world's cheapest labour, and this is the saddest thing of all the horrors that arise from Delhi's 15,000 inadequately regulated garment factories, some of which are among the worst sweatshops ever to taint the human conscience.

'Consumers in the West should not only be demanding answers from retailers as to how goods are produced but looking deep within themselves at how they spend their money.'