You can't have an FAC air pistol, it's Section 5, same as a .44 Magnum or 9mm Sig etc.
You may be able to get a restricted Hunting Master, but it would be a lot of hassle.
If you really want a large calibre airgun, get an FAC and then you can have a rifle, one of these would be nice. Barnes Pneumatic
Works of art in different calibres and 80 ft/lb or more, now that would kill a coke can
Or a cheap way would be get a Stealth and 9mm it, very popular in Holland.
Ben