There was serious talk a short time ago about introducing physiological testing to the licensing system, including some pretty invasive mental health questions.
And, to be honest, I'm not against that. I know several people with firearms certificates that I do not believe should have them. I know they are prone to temper and even physical violence - they should never have been issued with one in the first place IMO. Another one, who walked through my land with a shotgun with breech closed and pointed it at me saying 'it's OK it's not loaded' when I challenged him, the local gamekeeper said 'Oh, he's OK, he's not all there at times'!