But the regulations say you have to obey the aerodrome operating minima which in turn has to be approved by the state.
No, they don't say that the aerodrome operating minima have to be approved by the state. Approval is only required if you wish to conduct Low Visibility Operations (landing with an RVR less than 550 m). If the state has notified AOM for a particular approach, you cannot choose lower AOM. If the state has not, you may select your own AOM. States generally do not notify AOM for other than runways with instrument approach procedures.
Equally, by your logic, it would be legal to descend from safety altitude on some half baked procedure, then pick up a published approach,
So far so good -- that's not significantly different from vectoring.
[then arrive at minimums without the required visual references and still legally continue, merely because it was 'for the purpose of landing'.
No, that aspect is not permitted by NCO.OP.210(e):
NCO.OP.210 Commencement and continuation of approach — aeroplanes and helicopters
(a) The pilot-in-command may commence an instrument approach regardless of the reported runway visual range/visibility (RVR/VIS).
(b) If the reported RVR/VIS is less than the applicable minimum, the approach shall not be continued:
(1) below 1 000 ft above the aerodrome; or
(2) into the final approach segment in the case where the decision altitude/height (DA/H) or minimum descent altitude/height (MDA/H) is more than 1 000 ft above the aerodrome.
(c) Where the RVR is not available, RVR values may be derived by converting the reported visibility.
(d) If, after passing 1 000 ft above the aerodrome, the reported RVR/VIS falls below the applicable minimum, the approach may be continued to DA/H or MDA/H.
(e) The approach may be continued below DA/H or MDA/H and the landing may be completed provided that the visual reference adequate for the type of approach operation and for the intended runway is established at the DA/H or MDA/H and is maintained.
(f) The touchdown zone RVR shall always be controlling.
In a country where the state pays for countless IAPs to small airports, I can just about understand a rule that makes their use obligatory. In the UK approval and publication of an approach procedure offers significant value in mitigating risk. But that does not mean that a trajectory to landing without that £30,000 stamp of approval is not safe
enough.