Circular 01/2008 used the term 'core services' to describe the existing network of motorway services, with new services being 'infill sites'. New services which are more than 40 miles from existing services will also be designated as core sites.
Applications for a new core services don't need to provide an especially detailed demonstration of the need for new services.
The policy was updated in 2013, and the revised version dropped all references to the term.