Thanks, Rusty. I never would've found that explanation on my own.

Do the residents complain much? I know folks in the US **** and moan a lot
about such type of flying here.

The MOD page says: "The UK Military Low Flying System covers the open
airspace of the whole of the UK and surrounding overseas areas from the
surface to 2,000 feet above the ground or mean sea level."

Very general. Do they, in practice, designate certain areas that they use
for low flying? Else, how do they safeguard against intrusions by General
Aviation?

Tom