Basically anything hazardous and also certain materials that for environmental reasons need to be disposed of separately. Here is a list of the most common things you cannot put in a normal skip. Always ask if you are unsure or need to dispose of hazardous items.
Electrical equipment (WEEE), TVs & computer screens, Fridges/Freezers, TyresPaint & Paint cans, Gas Bottles, Asbestos, Clinical or medical Waste
Fluorescent Tubes, Solvents, Liquids, Oil, petrol, diesel, Batteries, Plasterboard. Hazardous & Toxic Materials.