Yes, that's true. There is also great interest in the AirSoft full-scale replicas of military firearms such as submachinguns and assault rifles. Some of those replicas even feature realistic fully-automatic fire and can cost thousands of dollars. Like the paintball phenomenon in the U.S., there is an interest in such "action pursuit games" in the U.K., but they use the super-realistic AirSoft gear to sting one another. "Real" airguns in the U.K. (and probably in continental Europe) must be regulated to keep the muzzle velocity/energy below some stipulated level. As you pointed out, "enhancement" is possible, but probably carries a hefty penalty if you're caught with such contraband.