Halesandpace the UK firearms legislstion has provision to issue a handgun FAC to an indivdual but the aplication has to go to the very top of the home office and so is very hard to get and only issued to people who are under a direct thret or in goverment related buisiness.
If the it was the goverment will to arm aircrew then they would just make the crews temporary police officers when on duty and solve the problem of issuing a FAC to each pilot.
As for myself i dont need a gun as now the rules have changed and i no longer have to apease hijackers i have all the weapons that i need in a standard aircraft and befor you ask im not going to say what i would do on an open forum like this.