No firearm is anything basically more than a shotgun that holds 2 cartridges 3 in a pump / auto, there's loads of variables including air weapons over 6 / 12 ft lb and you can own perfectly usable antique rifles without a license.
Holding a firearms license is pretty much specialist, you have to attend safety courses and have a reason for each firearm you want to own.
Actually in the eyes of the law, even a sub 12ftlb air rifle is classed as a firearm.
A firearm certificate is required for an air rifle above the 12ftlb legal limit (6ftlb for a pistol)
I would not say holding a license is specialist, you simply need to justify the reasons you wish to posess a firearm.
In my case i required 2 x .22 rimfire rifles (one as a dedicated NV rig), a .17 HMR for longer range work, and a .22 FAC air rifle for close range work around farm buildings. My shotguns (on a seperate certificate) are another matter and you do not need to provide reason for owning each one, only why you wish to own one in the first place and where you will use it / what for?
The local firearms officer will conduct an interview with the applicant to ensure suitability and check details regarding land permissions etc and no training courses are actually required although any previous experience shooting is always a big help when mentioned on the application.
Once a certificate is granted then it will be classed as a closed cert and you may only use the firearm over land which has been authorised by the cheif constable of that force. This remains the case for te first 5 years (normally unless you have a very good reason).
After that, then an open certificate is granted and the owner makes the informed choice regarding suitability of areas to shoot over (as long as they have the land owners permission)
No idea about antique rifles etc as never owned one although if ammunition is available for them then i suspect they will almost certainly need a deactivation certificate.
I would have thought it obvious that you must have a reason for having a firearm with you at any time. unloaded, in a slip or case etc.
It is acceptable to leave a firearm in a vehicle during a trip out as long as adequate steps are taken for security (in the boot out of sight is fine)
Most of the laws surrounding firearms are just common sense and if people need to question them then they are clearly not suited to owning one.
I plan all my shooting carefully, which rifle/shotgun or combination i will be using, firearms in bags in the boot and seperate from ammunition, license and permissions with me at all times.
Tresspass on to land with a firearm bagged and loaded or not is a serious offence, this applies to the full spectrum of what are considered firearms.