Here are some useful links

National Small-bore Rifle Association (NSRA)
The national governing body for all Small-bore Rifle and Pistol Target Shooting in the United Kingdom, including Airgun and Match Crossbow Shooting.

National Rifle Association of the UK (NRA)
Promoting target shooting throughout the United Kingdom.

Muzzle Loaders Association of Great Britain (MLAGB)
The Governing Body for muzzle loading within the UK.

Guidance  on Firearms Licensing
Home Office guidance to Police forces in the UK.