HWD
Ah yes that 2002 leaflet from the CAA.
Firstly, this is not LAW. The bit which applies to OCAS is advisory.
Most of that leaflet is concerning IFR navigation in CAS. The bit about BRNAV is correct,
AFAIK, and it's funny to note that in the GA context (no INS available) a BRNAV GPS is the only way one can fly in the airways.
Also, some of it doesn't make sense, e.g. 3.1.3.1 which assumes that when IFR OCAS one is always within the DOC of a navaid, which isn't the case.
3.2.1 is the one which anti-GPS people clutch at, I think. What does "operations shall be predicated on" mean? This is vague rubbish. What does "supplemental aid" mean? Does it mean that you are supposed to map read and ignore the GPS until lost? No, it doesn't mean anything really.
3.2.2 likewise.
How does one navigate IFR OCAS, without a radar service? Map reading isn't practical, nor is it practical at 3km vis which a PPL can fly at "VFR".