Anotherthing-
I am no longer in NATS but during my 10 years there we never discussed the A/P during TrUCE and neither do we now, however I am Twr/App and not speaking to a/c generally above FL140 if I can help it, so possibly we follow different
curriculums .I stand by my comments re the poss reasons for the non standard reply though. It doesn't excuse it,but possibly explains the thinking behind it.
edited to add
Although it is obvious the A/P would need to be disconnected, it probably isn't the first thing to come to mind when you hear those dreaded words