MIG gurgled happily, sounding much like they
were saying:

That was certainly my first thought, but I completely and utterly fail
to comprehend any circumstances where blocking an ambulance service
fast response vehicle, then locking gates on them, because they
"shouldn't be driving on the grass" is even remotely acceptable.

The story doesn't do itself much credit. It repeatedly refers to the
car as an "ambulance", despite it being one of these
http://www.ukemergency.co.uk/ambulance/dsc10899.jpg.

Yup, an ambulance service fast response vehicle, staffed by a paramedic.
The vehicle they send so as to get expert medical help to an incident
faster than a full-fat ambulance may be able to get there.