Huge differences between the US and UK for night operations....for all intents and purposes....there are none in the UK.
Now the response will be...."OH Yeah!" and they will quickly point out the Plod (Police or Po-leece) do them all the time. Private Operators....of which there are literally a hand full in the whole place....do not operate after dark (unless I am grossly mistaken).
Canada has a very enviable safety record....thus we might look to the North for some ideas.
The UK EMS folks are just as dedicated as their mates around the Globe...but the CAA/JAA/EASA or whatever authority that is in control at any given day...severely limits Night and IFR operations to the extent if you get injured at night in the UK you will in all liklihood be transported by ground.
A question has been posed....."What is an acceptable Loss rate in lives and aircraft?"
I turn it around...."What is the acceptable loss rate in patient lives that are lost due to the absence of a 24 hour HEMES operation?"