Why can I recycle some kinds of plastic but not others?

You can't bunch plastics together and recycle them. There are hundreds of varieties, all made from different polymers, and you'd end up with a low-quality, useless material. PET (polyethylene terephthalate) plastic - used in plastic bottles - is the easiest to recycle because it is made from a less complex mixture, according to Paul Davidson, the plastics sector manager at WRAP, the Waste and Resources Action Plan. “Plastic bottles are less likely to have any residue that could cause a problem for the machinery or affect the quality of the material coming out the other end,” he says.

Look for the number inside the triangular symbol on the bottom of plastic bottles; this is your guide to whether they can be recycled. Contact your local authority or check on its website to find out which numbers it is able to recycle. Most recycling centres take any bottles with numbers 1 to 3.

The problem is mixed plastics, due to the number of polymer types within them, such as in yoghurt pots, plastic meat trays and other materials that few doorstep collection schemes will take. If you're lucky, your council may have found a way of sending its low-grade plastic to a reprocessing unit where it will turn waste into insulation material or more packaging. But for most of us, this is the stuff we send to landfill.

It's fair to say that plastic recycling is not a green success story, but there is hope. WRAP has announced that it aims to have the UK's first mixed plastic reprocessing plant running by 2011. It also published research that proved for the first time that it was economically viable to recycle low-grade plastic as well as there being clear environmental gains. This at least answers cynics who claim that recycling plastic is a waste of money and energy since plastic is so cheap to make.