The Recycle Mate team receives a lot of questions about lids!
In some councils, rigid plastic lids (smaller than a yogurt tub lid) must be removed from the bottle/container and disposed in the general waste bin. This is because they are too small for processing and will slip through the gaps in collection and sorting equipment.
In other council areas, it is best for the lid to be left on so it can be recycled with the container.
There are also many charitable organisations and school groups collecting #2 and #4 plastic lids to be shredded and made into new products.
Wherever you are, the best advice - if in doubt, check it out! Use the search function on Recycle Mate to lookup items like "plastic milk bottle tops" and get the best recycling advice for your local area.