As a side-note (but still relevant for the original poster) remember that non-NATS units will consider any ATCO applicant when there is a vacancy, but NATS will not even consider qualified non-NATS ATCOs for their vacancies, unless you are personally known to the unit in question. Not an issue if you want to work at another ANSP, but a real problem with career progression generally, especially in the south of England.