I think people refer to it as the QXC as it is described as that { correctly or not } in the syllabus.
The United Kingdom
National Private Pilot Licence
(Simple Single-engine Aeroplane) (SSEA)
Syllabus
NOTES
1. The Solo Navigation Briefing Certificate is to be left at the base aerodrome, when
completed.
2. The student should carry the NPPL (SSEA) Qualifying Cross Country Certificate on the
final qualifying cross country flight and return it duly completed to the authorising
instructor.
This syllabus, for the National Private Pilot Licence Simple Single-engine
Aeroplane (NPPL(SSEA)) conforms to the agreed requirements of the
United Kingdom Civil Aviation Authority (CAA) for the training of pilots
for the grant of a UK National Private Pilot Licence (SSEA). This syllabus is
acceptable to the Authority.