Great system! I rang Birmingham. They told me to take my last lens packets to my local optician and ask for some more of the same. I went to SpecSavers. They told me (as advised earlier in this thread) that they must have a current signed prescription. Otherwise, make an appointment and pay £20 for the consultation before the lenses can be ordered.
BTW, another reason for aircrew needing to wear lenses is ejection. You are quite likely to lose specs, and damage yourself at the same time. If E&E is necessary, imperfect vision and facial damage are not helpful. Contact lenses do remarkably well in ejection. They started to become fairly standard for Harrier pilots with the advent of the GR7 and night ground attack, as the number of optical devices between the pilot and the target got greater.