The Scottish HEMS is paid for by the government, although the aircraft are leased, I believe. England & Wales are paid for by charities.
2 police units do night HEMS: Sussex and Wiltshire. N Wales used to, but I believe may not or only occasionally now. There are limitations imposed, as you might expect. Neither of these HEMS Units uses NVG, I believe. (N Wales does use NVG).
All UK police units can do CASEVACs (which is last resort, saving life, land and scoop) stuff. Some do a fair amount, some hardly ever.
I am not sure where the police NVG Units are exactly, these days. They were initially limited to only using NVG above 500 ft, and not for landings (DUH), but there was a move to progress to landing on NVG at some point.
Nuts