To be a “core participant” you have to have a significant role in the Inquiry. A core participant could be a person, a group, or an organisation. The significant role could be about all or only some of the things the Inquiry is looking into.
A core participant is more involved in the process of an inquiry than a member of the public.
To become a core participant you need to apply to the Chair of the Inquiry. At the end of the protocol there is an application form.