The CIL process begins when a planning application is submitted, you need to submit 'Form 1: CIL Additional Information' with your planning application.
The additional information form asks for details of new floorspace to be created by the development, and details of any floorspace to be demolished, which can be offset against the new floorspace calculation. It is in your interest to provide this information, especially where there are existing buildings in use on your site, to ensure that the CIL calculations can be completed correctly.
If the application is CIL liable, 'CIL Form 2 – Assumption of Liability (PDF)' will be required at the same time.
In some cases, proposals liable for CIL can be commenced with Permitted Development. When this is the case it will be your responsibility to inform the us using 'CIL Form 5 – Notice of chargeable development (PDF)' before commencement of development (including demolition) begins.