Just a final update on this situation.
The SS has contacted me to say that it it has been mentioned to him by powers on high that I referee the scrum engagement process in matches, beyond the agreed protocols. Being aware of the situation, he made it clear that this was in one particular match and as a result of a set of particular circumstances of which he was fully aware.
Nevertheless, he has been instructed to suggest to me that under similiar circumstances, I must not exceed the agreed protocols for scrum engagements as a referee. The correct situation should have been - as stated by someone on this thread, well done - to have abandoned the match on the grounds of referee injury! I am sure that would be a soft sell to the players concerned.
Ridiculous in my opinion, but indicative of the world we currently inhabit!
NM