As for Red 1 seeing the a/c in the TRA why was he not informed earlier by the appropriate radar unit? Surely the Reds were in receipt of some kind of service from the nearest military radar or were they assuming that the TRA would protect them from idiots (oh and birds)?
However, it is very obvious that many controllers these days have an aversion to use of primary Radar except when it's very quiet. Since it's highly unlikely that the villains of this piece were squawking (except maybe the birds, and then almost-certainly on the wrong frequency and not loudly enough) it's entirely possible that a controller won't have seen them.
About a year ago I saw a microlight make a precautionary to a prohibited disused airfield under Solent CTA from within Bournemouth. I reported it to the Solent controller who had clearly had no sight of the aircraft in question on his Radar at-all.
G