No its not compulsory. But its advisable.
Here in Wales we have been very good at recycling and have nearly met our targets. There are ever increasing landfil charges so if we dont recycle we will start paying for it through our council tax.
Fortnightly collections have forced people into recycling as people dont want bins full of waste going foul sitting around. With food and recycling collected weekly, only soft plastics need to be in the black bins.
The sooner the council brings in 3 weekly collections the better.