Flyingforfun - I think you're right. My employer's ops manual says:
Commencement and Continuation of an Approach
The Commander of an aircraft who receives information that the RVR is less than the specified minimum may continue an approach to land provided that:
When he receives that information the aircraft is below the outer marker altitude or equivalent position, and
The specified visual reference for landing has been established at the Decision Altitude/Minimum Descent Altitude and is maintained.
Note: Where no outer marker or equivalent position exists the pilot in command shall make the decision to continue or abandon the approach before descending below 1000 ft above the aerodrome on the final approach segment.
Note 2: The equivalent position can be established by means of a DME distance, a suitably located NDB or VOR, SRE or PAR fix or any other suitable fix that independently establishes the position of the aircraft.
I would think that's been written to cover the UK and ICAO versions.