Ah, now issi and Ethics have taken the lid off something that I didn't want to mention in case it clouded the issue (if you'll excuse the expression).
CAP168 is, technically, a set of rules that you need to satidfy in order to get an aerodrome licence, issued by the CAA's Airport Standards Department, and it doesn't have a lot to do with how aircraft are operated - that's down to the CAA's Flight Operations Department and what they will approve in your company's Ops Manual (all this is, of course, valid for the UK). Now, the two departments do talk to each other but maybe not as much as they could.
In order to get an aerodrome licence you have to show that you expect to offer all of the requirements in CAP 168 but it is recognised that some things might break from time to time, in which case the airport issues a NOTAM and the pilots then decide what they can do guided by their Ops Manual. For example, if some of the approach lights fail most Ops Manuals will still permit an approach, albeit perhaps with increased minima.
It's not quite so clear what the text that issi quoted actually means. Is it 'You won't get an aerodrome licence that permits you to offer Cat II/III approaches if you don't have IRVR but if the IRVR breaks you can report HO RVR or met vis and let the pilot decide what to do' or does it mean 'No IRVR = no Cat II/III'. The interesting thing is that you'll get a different answer from different people at the CAA.
As a pilot, what matters is what your Ops Manual says and if it is unclear on this topic I guess you should ask for it to be clarified. Although, if ATC at the airport are told that they cannot offer Cat II/III approaches without RVR you don't get the option!!
Knowing how inaccuarate HO RVR can be, maybe it is best if IRVR is available but this leads on to another debate about whether it all makes any difference anyway because if you get to DH/DA and don't see what you need you'll go ound. Because minima are just a tool to control exposure to the increased risk associated with a go-around if there is no chance that you'll be able to successfully complete the approach and landing.......