Carriage of imitation firearms is permitted only as checked-in luggage and only if the airline approves carriage.
If a toy or replica firearm could be mistaken for a real firearm then it is considered to be an imitation firearm.
As it is almost impossible to tell the difference between imitation firearms and real firearms the response from security agencies will be to treat the gun as a real firearm.
If you are found in possession of an imitation firearm on your person or in carry-on luggage:
You will be asked to relinquish all dangerous or prohibited items found in your carry-on luggage. If you refuse:
We x-ray bags going on planes to make sure there is nothing dangerous in them. If something comes up on the x-ray that needs checking, the bag will be opened, searched and any dangerous or prohibited item will be removed.