A friend of mine works for Wavin. A huge company that sell drainage systems amongst other things. He has just popped around with a new set of products called Recycore Technology. What they have done is to encase recycled plastics into virgin plastics so that the pipes end up with a 50% recycled content.
Up until now all pipes had to meet a standard that demanded the use of virgin materials, but they have changed the Kitemark standard so that they can use recycled materials, but get the same performance and quality and the same price. Win win.
So if you are looking for drainage products either above or below ground then it might be worth stipulating a recycled content as otherwise it will probably be the same old virgin plastic products. More info is available from www.recycoretechnology.co.uk