A Consumers Association (of Which? as its now known as) report suggests that £12 million could be saved on Council Tax bills by reducing the amount of contaminated recycling,
About 5% of recyclable items collected on the doorstep are rejected, but which.co.uk found that some councils rejected more than twice that amount. Councils that use co-mingled collection systems, where materials are collected mixed together, generally have higher rejection rates than those that operate a kerbside sorting system.
Recycling is rejected when it is ‘contaminated’, for example if people put the wrong materials in the wrong bin. which.co.uk says that improved collection systems, clearer information about how to recycle, and more careful recycling by consumers could reduce the amount that ends up in landfill.
It costs councils more to send rubbish to landfill than it does to recycle it, so the more people recycle successfully, the lower council tax bills should be. Sending rubbish to landfill will cost £620m this year in England alone.
The full report isn't available online. I suppose the advantage of co-mingling is that the total volume of recycling is increased as it is very simple for us to put all the materials into one bag.