<<I understood that LHR ATC have a standard pro forma that they read out to aircraft in distress notifying/asking them of the risks of overflying built-up areas?>>
Nope. Certainly nothing to that effect in the tower. The captain is always best placed to decide where he should put his aeroplane and we are just there to provide any assistance we can and generally keep everyone else out of the way. If the incident occurred a long way out and they were overflying other suitable airfields then the aerodrome authority would rightly want to question if Heathrow was the best place but at the end of the day it's the decision of the guy at the pointy end with the big hat and in this case, a job very well done.