Ah, so over there the big bore air rifles are legally the same level as having an actual cartridge type firearm.
In the Americas, the only place that really does that is Canada and a couple of former British colonies in the Caribbean. In most places they have about the same legal status as a slingshot, even in Mexico.
Unless you order over the web or find a shop that carries them, most of the pellets available locally are the flat head type Crossman pellets you get at Wal-Mart, either .177 or .22. However, I've found that they work fine on smaller game, especially tree squirrels and birds. Air rifles or a high powered slingshot are best for harvesting squirrels out of trees, especially in a populated area. When you are shooting upwards with a .22LR (which is approaching overkill on a squirrel) and you miss, you have sent a bullet on a parabolic trajectory over a populated area. However, I have relatives in Arkansas that shoot them out of the trees with a 20ga and think nothing of it.
Of the big bores, one of the most practical for here is probably the .45 caliber Korean rifles. A careful shot can drop a feral pig or a white tail deer. I like that all you need is a cast bullet, you don't have to rely upon powder and primers which a person can conserve if things get rough.
Yep, in th UK we are limited to air rifles roughly 1/3 of the power that a standard rifle is in the states (based on 30-40ftlb). If you apply for an FAC, you just really have to show the police you have somewhere to use it, a reason for doing so and it will be kept securely when not in use (in very simple terms).
Its maybe not such a bad thing with limited power, as there still seems to be the odd careless person around and tragic accidents have happend, even with reduced power.
I used to be a member of the Talon Owners Group, and had several shooting friends Stateside. The passion for air rifle shooting was just the same, despite a different culture.
Regards, al.