If not why? A domestic flight within the UK. I have the alternative of going with Virgin Trains if this is going to cause me unnecessary problems.
The item has been bought from here
This is clearly not allowed in hand luggage - nor in the checked in luggage. That is, you are not allowed to transport it by passenger plane at all. This page from the gov.uk site lists what's forbidden in hand luggage, related to weapons and ammunition (emphasis is mine):
You can’t take any of these items as hand luggage or in the hold:
- blasting caps
- detonators and fuses
- imitation explosive devices (including replica or model guns)
- mines, grenades, and other explosive military stores
- fireworks and pyrotechnics
- smoke canisters
- smoke cartridges
- plastic explosives (including black powder and percussion caps)
- hand grenades
- gun cigarette lighters
I suggest you check the rules for train travel - it may be forbidden there as well.
If it is detected, you'll certainly have problems. They will ask you why you travel with such a replica. Even if you don't have bad ideas around it, one can certainly state that you could create a panic in the plane if someone sees it. So it will definitely be forbidden. It is the same as holding a fake gun in the street. People aren't supposed to know that it is fake. And even if you tell them it is fake, you could really create a big mess with this so yes it will be forbidden.