Cat 1 ILS minimums would mostly likely be 200ft height above the runway, they could not be any lower but might be higher, I have only operated into Luton a few times and can not remember.
A cat 1 approaching can be manually flown or with the autopilot engaged. At my company the auto pilot must be disengaged at or above a height of 150ft on a Cat 1 ILS approach. As mentioned above for a Cat 2 or Cat 3 approach the autopilot would be used however once visual with the runway or approach lighting you can choose to manually land the aircraft.
Obviously the cloud height can vary so a Cat 2 or Cat 3 approach with a much lower decision height, the height above the runway at which point you have to be able to see the runway or some of the approach lighting, would substantially increase the chance of successfully completing the landing. A Cat 2 approach would typically have a decision height of 100ft or above and for Cat 3b in the UK the decision height can be 0ft, on the aircraft I fly you quite literally do not need to be able to see anything until the aircraft has touched down.
As I mentioned previously I have only been to Luton a few times but if these charts are accurate, they are quite old, then it appears to not have a Cat 3 ILS, being Cat 2 only. With it being on top of that hill I would be surprised if it does not have a Cat 3 approach.
https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.uvairlines.com/admin/resources/EGGW.pdf&ved=2ahUKEwijo-qN_snfAhUrz4UKHV9PDBgQFjABegQICBAB&usg=AOvVaw2pS72XZkuvVA614 17Cc2U_&cshid=1546257186410
I suppose the Captain really should have said "low cloud base" rather than "very poor visibility" but a low cloud base means that 'low visibility operations would be in force' with the ILS critical area being protected. Basically nothing could enter the critical area, another aircraft or vehicle, that could interfere with the localiser signal.
I found this from an old PPRUNE thread back in 2002
It's a popular misconception that LVPs are only associated with Cat II/III. At Luton we didn't have LVP as such until we introduced Cat II/III (Oct 92) but once we wrote the procedures we always went into LVP before we got near Cat II/II limits. Now we have to be in LVP and the runway safeguarded by the time the IRVR has reached 800m, in practice we start this at 1500m or more, depending how quickly the vis is dropping. Or the cloud has reached 200ft. . . .
As afterthelanding says, you may need to be in LVP because the cloud has lowered to 200ft or below, yet the vis is still good below it. This is why at Luton we introduced a half-way house we know as Vis 2. We use the Cat II/III holds but all the taxiway cl lights are on up to those holds. We only start full twy routeing when the vis drops to 400m or less (what we call Vis 3.) [Vis 2/3 does not equate with Cat II/III.]
Original thread is here
Low visibility procedures
Implementation of low visibility operations when the visibility drops to 800 meters and cloud base to 200ft is typical for quite a few UK airfields.
Do electronic items in use on the aircraft affect the ability of the aircrafts autopilot to fly the approach and auto land? I wouldn't know, you would have to ask an avionics engineer, but my airline, not Easy, want them turned off for every approach so please turn them off.