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