Someone is trying to reintroduce lynx in the UK (and in Keilder IIRC) but I don’t know how successful they’ve been so far.
Not very. They arent the best representatives of the rewild movement to be honest (although since they are keen on lawyers lets stop there). Which is somewhat sad since there really is a good argument for lynxes in order to keep the rather high deer population on its toes and under control.
You are right about chances of seeing them is about zero beyond maybe some tracks. Very shy and basically zero risk to humans unless you somehow managed to stumble into one which didnt spot you coming and had no escape route. Even then its interest would be in getting out of the way.
Golfchick: muntjac do bark which can be freakish but dont howl.
I do sometimes ride near a wildlife park and also a big cat sanctuary. At night or even day a big cat making noise is distinctly unnerving.