leaving aside Del Prado's comments -- an airprox, so far as i understand it from the CAA (and yes, I did check) is any incident where a pilot, controller etc believes there was a risk of an accident. in journalese "a near miss". a LOS = MOR = a near, near miss.
The CAA also told me that airproxes are down to the relevant professional's judgement. They told me there had been no airproxes in, i think, 2006.
But given a rising trend in LOS's, is it unreasonable to think that, unless checked, more serious incidents (even airproxes) could arise?
MORs, as the name implies, are legally required.