they should always work to an absolute minimum of 500 for a precision approach etc.
Perhaps the key word here is "should". Using this word merely emphasises that the AIP is a recommendation and not a rule. any statute imposing a requirement which would be backed by criminal sanction would use the word "shall". My wording was paraphrasing the wording of the AIP and not an attempt to manipulate it as DFC appears to think.
The point is this: what happens to a pilot with an IMC who descends below the DA/MDA before acquiring visual reference? What is the sanction? The answer is nothing happens to him, because the ANO does not prescribe any separate penalty or sanction for breaching the 500/600' minima. The AIP cannot create any separate sanction for breaching this "limit" because it is not legislation and cannot lay down penalties or sanctions as the ANO does. It is merely descriptive of the aerodrome limits. There is no separate and distinct limit for IMC rated pilots.
since they are minima and notified in the AIP, they are covered by Article 49.
They are not "notified". What Article 49 actually says is:
"an aircraft to which this article applies when making a descent to a runway in respect of which there is a notified instrument approach procedure shall not—
(a) continue an approach to landing on such a runway by flying below the relevant specified decision height; or
(b) descend below the relevant specified minimum descent height;"
So, the restrictions are defined by the "notified instrument approach procedure". There is nothing within the "notified instrument approach procedure" which distinguishes between the IR and IMC rated pilot. The "notified instrument approach procedure" is defined by reference to the design and layout of the aerodrome and its terrain. It is specified by the AIP for different types of approach and Article 49 is then applied by reference to that published procedure.
The question of whether IMC rated pilots are actually trained to descend below that altitude is completely separate. Nothing discussed here should be seen as an endorsement of ignoring the AIP. But the question was whether the 500/600' figure was
mandatory or advisory. My view is that it advisory. That is not to say I would ignore the recommendations.