QFI is a military term, and a now outdated civil term.
You are aiming to be a Flight Instructor (restricted) FI(R); and ultimately an FI.
At present in order to be paid, you will need a commercial pilots licence (CPL), on to which you add an FI rating. A class 1 medical is required.
The requirements are
here at this link in the CAA LASORS (Licensing, Administration and Standards) publication.
Specifically look at Section A General Information; Section D Commercial Pilots License; Section H, instructor ratings.