Book a flight on British Airways and the airline will calculate the carbon emissions of your journey. Pick up a chicken for dinner, and its label will tell you the amount of living space that the bird enjoyed before it landed in your supermarket.

But buy a T-shirt at many high street retailers, and you will learn nothing about the person who produced it. We now know more about the living conditions of the animals that we eat than the humans who clothe us.

The revelation this week by the cut-price fashion chain Primark that it was pulling orders from three Indian factories that have violated its code of conduct has again cast the spotlight on ethical sourcing.

Primark was right to come clean about suppliers that subcontract to unapproved facilities. But abuses like these are common in today's global supply chains. The larger problem remains unresolved - how little many companies tell us about how their goods are made. Their reticence belies an insincerity in their claims to social responsibility.

In the decade since the anti-sweatshop movement first alerted us to the underpayment of wages, excessive working hours and the use of child labour, global retailers have hired monitors to inspect their suppliers abroad so that they can reassure their customers at home. For some, a code of conduct is a placard that they show to the press to prove their innocence - or at least their honourable - intentions when scandal breaks.

In the two years that I spent researching consumer goods factories in China, I saw how our expectations of £2 T-shirts and £15 DVD players are driving factories to skimp on wages, worker safety and environmental protection.

Retailers want their goods cheaply and don't want to be tainted by media exposés. So factories, in China and elsewhere, give retailers their low prices and provide a veneer of compliance with companies' codes of conduct.

They coach workers to tell Western buyers what they want to hear and to cook their books. Falsification of payroll documents, which Western brands check during their inspections, is now so common in China that it has spawned a cottage industry of “falsification engineers”.

As Primark has reminded us, other factories use secret subcontractors, often called “shadow factories”, where conditions are much worse than in the facilities that the Western brands see. One factory manager I met called the factory that he showed Wal-Mart his “five-star factory” - as luxurious as a five-star hotel. Down the road, his shadow factory made the same products under very different conditions.

Falsification and the use of shadow factories allow underpayment of wages, excessive overtime and unsafe conditions to persist. The most progressive companies, including Nike, Gap and adidas, admit that they are grappling with these issues and describe what they are doing to address them.

But too many other retailers share only the smallest possible amount of information that will satisfy our curiosity. Many crucial questions remain unanswered.

A random sampling of UK retailers' websites proves the point. Primark's code of conduct, available online, fills barely half a page. In a company video available on the site, a woman's voice explains that “our prices are lower because our overheads are lower” and that factories “get a real buzz” supplying the retailer.

The upmarket clothing chain Reiss offers shoppers no information about its suppliers. When I called the company, I was asked to phone its finance director. The Next chain, which publishes a corporate social responsibility report, lists the number of hangers it recycles, but is strangely silent on the number of factories that it has cited for the use of child labour or unregistered subcontractors.

Surely this isn't for lack of experience in disclosure. Stock market listing rules oblige British companies to announce their financial performance. Companies are also becoming increasingly forthright about how they are reducing their environmental impact.

But why don't companies reveal more data about their performance in improving conditions for the workers in their supply chains? If their social responsibility programmes are as robust as they say, what have they got to hide?

We all deserve to know more. Consumers have been the driving force in convincing companies to tell us more about the life and times of our poultry.

That pressure has forced companies to start thinking about these issues more creatively. We have the power to do the same for global supply chains. All we have to do is to pick up the telephone, dial our favourite retailers, and start asking questions.

Alexandra Harney is the author of The China Price: The True Cost of Chinese Competitive Advantage (Penguin Press, 2008).

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