Look at somewhere like Bournmouth and you have a 'deep' built-up area prior to reaching the main crowd then display line. Perhaps a Hawk has the speed (energy) to fly clear following an engine failure but a Hurricane couldn't
I was at the Bournemouth show and thought that the number of boats just outside the box are getting larger with each year. I also spent some time on the top of Alum Chine during the Red Arrows display on Saturday and I estimate that the single aircraft was only 200ft above the cliff top heading north over the town.
I'm relieved to understand that there would be sufficient energy to clear the town if there was a bird strike.