If you wanted to be a sparky, you can do
- 16th - 17th ed update course
- Domestic Installer (Part P) if going domestic
- 2391 Inspection & Testing if going industrial.

Your time in the navy would be sufficient to cover the vocational element, so you would be able to register with the IEE still, if you wanted to. There is no requirement in law to have anything other than 17th ed to carry out commercial work, however the extent of work is limited by testing and design/documentation requirements.