I would say that your best option would be to try and get a job as an ATC assistant at an airfield where the ATC services are not provided by NATS.
NATS provide a great training scheme, but it's not as great a career as it once was.
Your background in avaition should compensate for the lack of academic experience, but be warned, the competition is strong, as most ATC managers now take on atc assistants with a
long term view of some of them being potential future atcos.
In the first instance, write to the ATSM (Air Traffic Services Manager) at every airport in the vicinity (the more local - the better chance you stand), enclose a brief but detailed CV and covering letter explaining why you want a career in atc and why you are the best candidate. Then follow it up with a telephone call a week or so later asking if you can visit the atc unit and also fix an appointment with the ATSM during the same visit - even if they have no vacancies. Be polite, but persistant.
SERCO run most of their recruitment of "ab - initio" atc staff on the same basis, and if you're considered good enough, you'll be put forward for the aptitude tests and future training in due course.
You could try Highlands & Islands Airports, but they tend to recruit ab initio atc staff directly from the local population, or their own staff.
Good luck.
