Burnie
Thanks for embellishing my understanding of obstacle limitation surfaces. You will see that I made an assumption - that MoD try to apply the CAP168/ICAO criteria - in full knowledge that this seldom happens in reality; perhaps I should have typed more slowly to indicate that I was describing a hypothetical scenario. Hence my use of the modal verb "should" rather than "shall" (in ICAO meaning "ought" and must" - except that the preamble to Annex 14 urges Member states to apply the former - used in Recommended Practices with the same weight as the latter, used in Standards - SARPS).
You will also have picked up that the runway strip - 300 metres wide and 60 meteres before the threshold - provides the origin of both the approach surface and the transitional surface (the latter's origin at the longitudinal extent of the strip, it is a 1:7 slope).
I haven't been to Waddington for some time (since I left 101 sqn in 1975 to move up the road to Scampton), but I do recall that the the A15 was/is close to runway 20 threshold and the adjacent taxiway; in fact so close as to infringe the runway strip, including a good portion to the south of the southern set of traffic lights (and the aerodrome boundary fence).
Just as well that the military OLS do not fully embrace the civil criteria (Northolt is an even more striking example of where the criteria are not met). I'm sure that more differences would be revealed if one were to make a more detailed inspection of the infrastructure. I base this last satement on 12 years employment with the CAA as an aerodrome inspector, which included the transition of Farnborough, Finningley and St Mawgan from military to civil licensing criteria and an MoD requested inspection/audit of Northolt in December 2008.
Mister B
Happy to expand and clarify any technical questions, cognizant (and that's the first spelling option in the OED) that the ambition of MoD to apply civil criteria is often constrained by, financial limits, topography, operational needs, etc.