The approach ban is not a "European" or "UK" issue.
The approach ban is an ICAO standard and applicable to General Aviation Operations. ICAO Annex 6 Volume 2 refers.
In simple terms,
An approach can be started regardless of the weather.
The approach can not continue beyond the Outer Marker or equivalent position (precision approach) or descend below 1000ft AAL (non-precision approach) if the weather is below the applicable minima.
If the aircraft has passed the Outer Marker or is below 1000ft AAL and the weather deteoriates below the applicable minima the approach can be continued to the DA / MDA.
Regardless of weather conditions the aircraft can not continue the approach below the applicable DA / MDA unless the required visual references are visible and continue to be so.
The UK has decided that private operations shall use the minima etc published in the AIP which are aligned with EU-OPS (the standards for commercial ops). Therefore G reg operators and all other operators when in the UK must comply with the requirments.
A quick look at the GEN section of an AIP will tell you if there any differences from the ICAO standard.
Commercial flight guides may also have this information.
RE 800m single pilot limitation.
It is an RVR of 800m.
If RVR is not reported then it is permitted to obtain an equivalent figure by converting the met visibility based on certain criteria. As others have said, in certain cases the visibility can be multiplied by 1.5 to give a CMV of 800m.
There is nothing to gain from this because if RVR is reported then that figure has to be used. If RVR is not reported then the CMV will usually be a figure very similar to that which would be reported as RVR.
Again, no matter how far above minima the RVR is (or the CMV is) if you don't have the required visual reference at DA you are not going to land (legally).
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So you have a lower DH minimum without an A/P !!!!
Not necessarily. Imagine the same calculation with a certified autopilot where the minimum use height was 100ft.
or
Imagine using your autopilot with minimum use height of 200ft when the DH is 250ft.
There are plenty of ILS's where coupled approaches are not allowed or are not allowed below a height that is higher than the DH.
However, it is not simply about how low you can go. With a suitable autopilot the workload is a lot lower and one can (while fully monitoring the approach) spend a lot more time peering into the mist for the approach lights than if one hand-flies.