Firstly, anyone who stores a firearm in a loaded condition is a fool. If anyone takes a weapon to an airport intending it to be boarded on an aircraft, not knowing that it is loaded is a fool. Furthermore, anyone who thinks that the way you prove a firearm is unloaded is by pulling the trigger is criminally negligent. That the US Constitution allows such people access to firearms is disgraceful.
Yes, in the UK you need to show that a firearm is unloaded. This is normally done in a discreet area, away from the check-in desk, with police or security staff, or both present. Not by taking it out, showing it to the check-in agent and pulling the trigger.
StbdD, that quote came from the article itself, which you clearly haven't read.