CIL was introduced in 2008. It is a charge levied on people who gain planning permission for many types of new buildings. It only applies to England and Wales and not all councils charge CIL. The rate is charged per square metre of floor area and can also vary a lot between councils, ranging from anywhere between £10/m2 to £575/m2. The money raised from CIL is used to improve the local area. By funding amenities like hospitals, schools, parks and public sports facilities.
The developer is the one who has to pay the charge. It is due on commencement as given in section 56(4) of the Town and Country Planning Act 1990. Commonly accepted as the time where work begins to prepare the site for construction. Including demolition, pipes being laid and so on. If CIL is charged in a particular area, all new houses, flats and extensions larger than 100m2 will likely involve a CIL charge.