Cartons

Milk is packaged in a few different ways. Fresh milk, which isn't stored for as long, is typically packaged in recyclable materials like card and hard plastic. Long-life milk, which has to be shelf-stable for much longer periods, is packaged in Tetra Paks which aren't recycled. 

Liquid paperboard cartons - Yellow bin
Small volumes of fresh milk and flavoured milk drinks are packaged in liquid paperboard. Liquid paperboard is a composite material of paperboard sandwiched between two layers of very thin plastic.

Tetra Paks (long life cartons) - Red bin 
Long life milk and non-dairy milks are packaged in Tetra Paks. Tetra Paks are a composite material of paper, plastic, and foil. These aren't recycled so go in the red general waste bin. 

Reuse tip: Refillable glass bottles are the gold standard when it comes to waste reduction. If a refill service isn't available to you, opt for milk packaged in recyclable materials.