One wonders if this gross cockup had anything to do with the departure of Charles Clarke as Home Secretary shortly afterwards (terrorist security is still a National concern, not the Scottish Parliament).
I am glad that the Irish Govt has raised it at government level so it won't be glossed over.
Bearing in mind this flight was Beauvais - Dublin, if the threat occurred in UK airspace they must have been near either the West Country or West Wales. To divert to Prestwick from there would take quite some time (in fact possibly Stansted, the other security alternate, would have been closer). If the authorities at Prestwick cannot marshal their people into place in that time then it shows that Prestwick is the wrong airport for such diversions.