All right. I've recovered my composure enough to type again…
Aerodrome operating minima are established for aerodromes
for take-off and landing. They consist of a decision height or minimum descent height and an associated visibility condition for each approach. Aerodrome operating minima may be published by the state, although these days the UK simply adopts what it says in the corresponding part of the EASA Air Ops Regulation, in this case Part-NCO.
The rule that you want to apply as "MSA" is in Part-SERA.
SERA.5015 Instrument flight rules (IFR) — Rules applicable to all IFR flights
(b) Minimum levels
Except when necessary for take-off or landing, or except when specifically authorised by the competent authority, an IFR flight shall be flown at a level which is not below the minimum flight altitude established by the State whose territory is overflown, or, where no such minimum flight altitude has been established:
(1) over high terrain or in mountainous areas, at a level which is at least 600 m (2 000 ft) above the highest obstacle located within 8 km of the estimated position of the aircraft;
(2) elsewhere than as specified in (1), at a level which is at least 300 m (1 000 ft) above the highest obstacle located within 8 km of the estimated position of the aircraft.
The 1000 ft mentioned in (b) is not part of "aerodrome operating minima". It is a generic rule for IFR flight that applies
except when necessary for take-off or landing.
Descent below the levels addressed in SERA.5015(b)(2) when taking off or landing is not to be taken lightly. The best way of mitigating risk is to use a PANS-OPS compliant instrument approach procedure if available. Almost all CAT operations manuals will require that if relatively conservative minima for a visual approach are not met. But there is no requirement that a published procedure is used to meet the requirements of SERA.5015(b) when operating under Part-NCO.