Alpha,
The link which EGBK has provided you with gives details of the UK approach ban - you must not descend below 1000' aal if the RVR is below minima, although once past 1000' you may continue the approach if the RVR subsequently falls below minima.
However, that is different to ICAO, which says (I think) that you must not continue past the OM or FAF if RVR is below minima, but once you've passed this point you can continue if it falls below minima.
I wonder if the difference between UK and ICAO rules is what's causing your confusion?
FFF
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