From what I have ben told when the recycling centre in Hertfordshire went up in smoke for the second time and burned for days is that it's simply running to hot with to much fuel feeding the fire and since on top of that it wasn't spreading they were quite happy for it to let it burn itself out.
I don't know anything about the wiltshire one.
The MET only do police ops. They are not even equipped for CASEVACs. Also their cabs are very heavy due to all the kit onboard.
You would be better to charter a helicopter with a bucket for the few times you need it...IMHO.
As for eastbourne didn't they have a boat on the water next to it pumping a fountain of sea water over the fire?