Shy, have a read of this:
Aerodrome operating minima (AOM) for IFR flights are set out in some detail. They are “selected and used” by the pilot-in-command. They cannot be lower than those established by the state in which the aerodrome is located, and cannot include low visibility operations (550 m RVR for approach, 400 m RVR for take-off) without a specific approval. Note that the 400 m RVR for take-off is higher than the 150 m required under the UK ANO.
AOM are in two parts:
Decision heights and minimum descent heights are specified in the implementing rules, and are calculated on the same basis as under most national rules and EU-OPS. The DH/MDH is usually the higher of the OCH or the system minimum for the approach aid.
Minimum RVRs and visibilities are set out in guidance material. In principle, the pilot is at liberty to select these within the constraints mentioned above. In practice, I suspect most will use those in the Guidance Material or published by Jeppesen, which are substantially the same as for CAT.
The author participated in the Part-NCO review group in 2010, working with EASA and other stakeholders on the text of Part-NCO.
It is pretty clear to me that whatever discretion private operators had to exploit homebrew approaches back in the day no longer exists.