To be clear, what follows is an attempt to dig to the truth, not a dig at you. I am striving to be technically correct - the best kind of correct.
That's not what VCRA S38 says. The word belief or believes does not appear all, and it explicitly, unambiguously, without a doubt does require a RIF to look like a "real firearm". I "quote" this because that's what it says, and it goes on to define what "real firearm" means, using the phrases "actual make and model of modern firearm" / "actual modern firearm", and further defines "modern firearm" as distinctively post 1870.
That's distinct from the Firearms Act 1968 definition of "imitation firearm" which is much broader: “imitation firearm” means any thing which has the appearance of being a firearm.
https://www.legislation.gov.uk/ukpga/1968/27/section/57
The Firearms Act 1968 definition applies to possession in public. The VCRA definition applies to importation, sale, manufacture or modification, which is what we're interested in here.
We disagree over whether there is an exclusionary conflict, or whether both can apply. It seems that Border Force think the latter.
Policing and Crime Act 2017 makes an exception for airsoft guns only for the purposes of the Firearms Act 1968. There is no general exemption from other firearms legislation.
https://www.legislation.gov.uk/ukpga/2017/3/section/125/enacted
So that's neither here not there for any consideration of the VCRA.
Border Farce clearly didn't get that memo though, and I - reluctantly - agree with them. The law says what the law says, and it only says that "de-activated firearms" cannot be RIFs.
They're free to interpret it any way that they like, and it's going to take a court to decide. I hope that they turn out to be wrong.
Agreed, it does say "imitation firearm". But sadly, among the plethora of other definitions, it doesn't actually define "imitation firearm", and most particularly it doesn't provide an exclusive either/or distinction between "imitation firearm" and "firearm" (only "de-activated firearm").
As per that MP5 PDW airgun above, if you showed that to the aforementioned non expert and asked "Is that an imitation of a real firearm?" then what other answer would they give than "Yes, of course it is."
And it is. It really is. It's quite deliberately an imitation of a specific firearm, and the intent of the legislation is to keep those out of the hands of people who don't have a specific purpose that requires them.
It's also a firearm in and of itself.
The crux is whether a court will hold that it can be both, and until we get that verdict from the High Court or above (Magistrates' verdicts can be persuasive but don't set precedent), we're just not going to know.