Navs, I use the term deliberately although you may substitute your own nomenclature, are not just things you grow on trees or train using a corner of a squadron when there is time. As Pontius has implied, nav training requires an investment similar to pilot training. This is not something you can suddenly start doing without a great deal of investment, and that includes the appropriate cardre of folk with the experience and training to be instructors.
Why do you think Nav School at Finningley was such a big operation?
It would take a massive commitment to restart Nav Training. I doubt the RAF could do it any more and I'm pretty sure it will never be resourced, no matter how badly we need some new Navs.
It saddens me.