I am thinking that there should be a licence for these cross bows
I've got some sympathy for the viewpoint but there are several problems. Where to draw the line is first. Clearly "all crossbows" is the simplest, but that would include not only the 60lb medieval style bow I knocked up in my garage from scrap timber to pass the time, and has an energy less than an 18lb beginner
recurve bow, but also my son's toy that shoots plastic sucker darts. Unless the legislation was drafted very carefully.
Clearly there are cases of abuse, but where is the larger risk of abuse? A bow that costs north of £3.5k, or a basic one with a 120lb draw that costs less than £100?
Which leads me onto the bigger problem, that such measures would be brought in with a package of other restrictions, some of which are likely to be annoying, poorly thought out and quite possibly very onerous. As said above, there would be a temptation in some politicians to include compounds. Maybe only those capable of >300fps? Might sound reasonable at first, but even that's problematic. What if it's with a really light arrow so that it becomes only those <250fps with reasonable weight arrows? Just an example.
So all in all, it's really best not to go there at all.