Thanks for all the comments, it's made me feel a bit better at least.
I realise that landing before the threshold is a big deal, obviously it should never happen, what I meant was that it wasn't particularly unsafe on this occassion because of the basically unused taxiway prior to it (and the big area of grass before that) but still, whether it's safe in actuality or not, as I've said I realise it's totally unacceptable and a definite reason for a fail!
The testing officer has something like 30,000 hours and basically knows everything, he gave me a few anecdotes after the debrief all about the importance of go-arounds, so if one good thing comes to me from all this, it's that the attitude of "if in doubt, go around" has been drilled into my skull.