I don't think a normal eye test gives a return on investment high enough to get past NICE. Remember whenever the NHS spends money on one thing, they have to stop sending the money on something else.
Ummm.......remembering that you are not UK based.
If you are diagnosed as diabetic you get a free eye test. Used to be annually, may now be every two years, but you can have free eye tests more frequently if you have any reason to suspect it is necessary.
SpecSavers, for one, are usually happy to do on demand eye testing and they have plenty of electronic gizmos to measure your eyesight. They also take retinal photographs.
I had an additional appointment before ordering some fixed vision glasses because I felt that my prescription had changed due (possibly) to improving BG control.
As posted above, it is a good idea for all diabetics to have a regular eye appointment just in case.
It should be very clear that this is in addition to the DR screening offered as a stand alone service.
Edit: if you are saying that the cost benefits would not justify every diabetic in the country attending Moorfields Eye Hospital or the equivalent then I would agree. The usual NHS strategy is to filter out those not at risk early on, without taking up scarce resources in specialist clinics. That is why GPs and screening services are usually the first line of defence, along with well provided services such as opticians, and patients are only referred on if they have signs of problems. The word "triage" is nagging at me. Quick check to eliminate low risk, concentrate scarce resources on more serious problems.