Moggiee:
"As for cloudbase, the acceptable minimum on an ILS approach is 0'. "
Only for CAT III ILS approaches. CAT II approaches have a 100' cloud base minimum, and CAT I minimum is 200'.
ATPRider:
"Can anyone tell me if Ireland has "Absolute Minima" below which ATC must inform a crew that if they commence an approach they will be required to take reporting action? "
There is no such legislation in Ireland. There are published minimum RVR values (whether iRVR or HORVR) for each instrument runway, which are calculated using factors such as instrument approach aids and AGL etc. available for the runway concerned; but there is nothing to stop a crew making an approach to DH. It is very possible that the wx could have improved sufficiently on completion of the approach to make a landing possible where it would have been impossible on commencement! I have seen it happen. The onus is on the crew to exercise professional responsibility.
I am not speculating as to cause of this unfortunate accident - merely correcting an error and answering a question. I for one will await the official investigation report.