Jeezz.. is it still happening? It must be 20 years ago.. I was on watch as the Tower Supervisor and a 747 at 10 miles declared a medical emergency. I went through the standard procedure and was put through to the London Ambulance Service in Waterloo. I gave the operator the stand number at Heathrow which had been allocated to the a/c and I was asked "which road is that in?" The ambulance eventually turned up about 20 minutes after the a/c had parked.
Considering all the gyrations both ATC and crews go through to help medical emergencies it really beggars belief that ground backup leaves so much to be desired.