Nick hits it on the head; just because the procedures don't exist does not mean that they are not needed. I seem to recall the CAA have, or had, a "GPS Steering Group"; quite what they do or did is a bit of a mystery,
The CAA should have in place a sytem whereby operators can submit for approval a let down based on a predifined criterea. It should ideally be designed with VOR/DME crosscuts and if available an NDB beacon. When flown, use of a radar service should also be utilized. With all these and the acccuracy of GPS then accurate GPS approaches are very possible and safe.
If the CAA does not get it's act together, (there's a radical thought), then unapproved procedures will be flown with various outcomes; the Irish S76!
As to the original thread. Allowed to fly at 300 feet? Maybe on scene and with 100 feet cloud seperation, but in transit - I would think not. Check the POAM!