Thanks for all the responses, although the CAA "definition" wasn't really a definition - it only covered vertical separation for a start! A couple of points:

1) The captain said that the go around was due to the other aircraft and ours getting too close on the approach. (I guess I should have explicitly stated it in the OP, but thought it was implicit.)
2) I made no judgement as to how close the aircraft came (I've seen those youtube videos as well!) I was just wondering if a terminated approach because of "air prox" is a reported event or not.

rb211.