... a clear policy on intervention...
Double Bogey
That's exactly my point. Work out the (best practice) SOP. Train for it using all conditions and have the discipline and the mutual trust to use them properly.
Try to get away from the kind of thinking that's 'inside the box' that the regs have formed and think 'Airmanship' and what I call 'Educated Common Sense'. When you have designed what you hope is the perfect solution THEN check it against the regs and if in doubt ask for a derogation under 'equivalent level of risk management' if you are confident that it is right. Of course you would have checked it thoroughly in the sim first.
G