Expanded Polystyrene Foam (EPS), this is the one made up of what looks like little balls but polystyrene can also look like regular plastic and is very commonly used for the lids of coffee cups.
Expanded polystyrene is a material that can be recycled when separately collected, some civic amenity centres may accept it but be sure to check locally before you arrive.
Small amounts of polystyrene can be used in the bottom of plant pots before soil is added.
If you do not have access to a civic amenity centre who can recycle it then EPS should be placed in the general waste bin.
If it’s the the polystyrene used in a coffee cup lid this can be placed in your recycle bin.