as above, to bring the gun into the UK as it is, will require you, the owner, to have a valid defence as prescribed under the VCRA (Violent Crime Reduction Act) to demonstrate that you will use the RIF in a safe manner.
Lets put the airline aside for a moment, and concentrate on the legal side:
1) a UKARA
REGISTRATION (not licence, as Lozart said) is the easiest way to obtain a defence, though probably not possible given your situation. is it possible to leave the RIF with a friend or relative for a couple of months whilst you "earn" your UKARA registration?
2) there are other defences, which might be worth looking into, you can read the particular part of the VCRA
HERE and the amendment
HERE. On the second link, search for the word Airsoft and you will find what you need.
3) if you can paint the gun so that it appears unrealistic (ignore the myth about having to paint 51% of the gun) you can import it as an IF provided that you are 18 or older. just make sure that you apply come common sense, paint something that isnt covered when you hold the replica, and use a bright colour that doesnt incorporate a camouflage.
really, if i were you, id give the relevant parts of the VCRA and te documents in the second link a read, you should be able to figure out the best way of keeping your RIF that suits your own personal circumstances, and remember, most people on here will help you, just ask us
Welcome to our community
EDIT: the second part i forgot to write:
As for the Airline, they may well be a little nervous about allowing an imitation firearm onto an aircraft, but after explaining what you intend to do well ahead of time, and transporting the RIF safely should sort all that out.
First, ring the airline and ask if it is possible, explain exactly what you intend to carry, and make it clear that you want it to go into the hold, and not into the cabin with you
then make sure it is kept in a suitable container, id personally put it into a hard case, locked securely. you can expect the lock to be broken when you get it off the carousel, as the security teams at both airports will probably want to inspect it to ensure that it isnt real (use a TSA padlock and they can open it without breaking it). keep a note in the case that explains what it is, that it is incapable of handling or discharging any form of ammunition other than lightweight BBs, that its muzzle energy is at or around 1j and that it is used for airsoft skirmishing. if you dont paint it, put your UKARA details in there as well, including Name, Full Address, UKARA number and any other details you can think of
once you get to the airport, hand the case/bag over when you check in and explain what the contents are, so that they can make sure that it doesnt cause a scare later on down the conveyors
and most of all, think of everybody that will handle or see the case/bag after you hand it over, and make sure that they have no reason to keep it from you.
it goes without saying that the RIF should be inert, with no battery loaded and ideally, the magazines stored in a separate compartment or even a separate container
and NEVER
EVER
use the word "Gun" "Firearm" or "Weapon" at the airport, whilst youre carrying a gun bag or gun case. Also DO NOT remove it from the case. if the check in clerk or security ask to see it, explain that it is an RIF and that you should take it to a private room first
