I certainly agree that it is way beyond the control of OC Ops, however i really can't see that single engine ops are a risk, especially when you look at all the hawk movements round Valley etc without major system (engine, fuel, hyd's etc) failure.
If there was any risk Hawk movements would be restricted to only 'out of the way' airfields ----- mmm, like Valley, Mona, Leeming etc (ok, do the powers at be know something we don’t?). And yet the mighty Hawk can fly into virtually anywhere, I don’t know of any Hawk pilot who gets nervous flying from Malta to Cyprus over all that ocean etc, etc.
But you are right, an incident at Northolt would not be good, but to ban single engines seems like a very short sighted and uneducated edict.