When the world's largest container ship docked in Britain shortly before Christmas, its vast cargo of goods, from bingo sets to bras, epitomised the scale of imports from China. But when the MS Emma Maersk, dubbed "SS Santa", set sail on its return journey to Yantian, few noticed it was laden with Britain's fastest-growing export to China: waste.
A combination of the global economy and the boom in recycling in Britain, which last year generated nearly 7 million tonnes of recyclable waste, has created an inter-continental trade worth £460m. Last year, Britain sent more than 200,000 tonnes of plastic to China for recycling, along with 2 million tonnes of used paper or cardboard and large quantities of steel and redundant electrical goods.
It is a market generated by Britain's lack of capacity to cope with its own recycled waste and, more importantly, the thirst of China for "raw" materials, such as used plastic, to feed its booming economy.
The Environment Agency authorises a small number of exporters to send abroad "green" waste - recyclable products sorted into different categories. It insists the trade is "robustly regulated".
Such is the demand from the Far East, a trawl of plastic exchange websites yesterday revealed dozens of China-based companies willing to pay £300 for every tonne of bottles made from PET, the plastic used for water or soft drinks. In Britain, plastic recyclers can barely pay £100 per tonne.
At about £500 to send a 26-tonne container of waste to China, it is now cheaper to send plastic to the Far East than by road from London to Manchester.
Some experts argue that the trade in fact creates a virtuous circle. A consultant for one of the leading exporters said: "It sounds perverse but if you think about it we are using waste that would otherwise go to landfill, filling ships that would otherwise be empty, and creating business that would otherwise use virgin raw materials."
But the waste trade is not always virtuous. The Environment Agency has prosecuted several companies for attempting to export "green" paper waste mixed with normal municipal rubbish.
And the human and environmental cost to those who then pick through the waste is unknown, despite the insistence of the authorities that no harmful waste is permitted to enter the country.
Critics say sending the material across the planet is "barmy". A spokesman for Friends of the Earth said: "We would prefer to see this material recycled in Britain by expanding our own recycling industry."