I duno what would happen in a court but the 2017 law for airsoft is:
The permitted kinetic energy level is —
(a) in the case of a weapon which is capable of discharging two or
more missiles successively without repeated pressure on the
trigger, 1.3 joules;
(b) in any other case, 2.5 joules.
Even though air rifles have higher joule limits they are a different legal category.
And you know how courts stick to the law 😉
I know it doesn't make any sense that to buy an airsoft gun you need to show legitimate criteria but to buy a much more dangerous air rifle you can just walk into a shop or have it delivered 🤪