TCAS FAN is correct in his explanation of how the current 'uncategorised' UK ILS's will become CAT I and in most cases will benefit from a lower OCH, but surely the UK minimum DH for a CAT I ILS will remain at 200ft will it not?
SEN is in a similar situation but even with ALSF appoach lighting and runway centreline lights, plus IRVR, all to be installed shortly on runway 24 as part of the redevelopment programme, they still anticipate a DH of 200ft for a code C aircraft and RVR minima of 550m, those being the CAP 168/ICAO Annex 14 system minima for a CAT I installation.