Statement of Purpose: A Statement of Purpose is the document a CQC-registered provider must keep that sets out its aims and objectives, the regulated activities it provides, the service user groups it serves, and the addresses it operates from.
It is a legal requirement rather than a marketing document, and CQC uses it as the reference point for what you said you would do.
It has to be given to CQC at registration and kept current afterwards. Because inspectors compare it against what they actually find, inconsistency between the Statement of Purpose and your other documents is a frequent reason applications are returned: the regulated activities do not match the description, the service user bands differ from the policies, or the locations disagree with the application form.
Treat it as a live document. When you change what you do, who you do it for, or where you do it from, the Statement of Purpose changes too, and in most cases CQC needs to be told.