whatever is the most suitable for a bit of rabbiting really?
Short range (<30yds) bunnies and small areas of land: Air rifle sub 12ftlbs -no licence
Short to medium range (<60yds) bunnies: FAC air-rifle, .22LR Rimfire or other variants of .22 rimfire, excluding CB cap, .17Mach2. FAC needed.
Medium to long range (<120yd): .22LR, .22 win magnum, .17HMR (Hornady Magnum Rimfire) -head shots only if you want to eat them (and why wouldn't you?) FAC needed.
Long Range (be sensible this is live quarry! 150yd max): .17HMR. Centrefire calibres not included for sanities sake. FAC needed.
In addition to the bureaucracy and costs above, the land has to be approved by the police for use with any calibre/rifle other than sub 12ftlbs air-rifles, unless you have an "open" ticket FAC (which you won't get at first). Some land is already registered but the inspection lapses after a few years.
.22LR is the standard choice of the various rimfire options: efficiently silenced subsonic ammunition is quieter than many air-rifles.
I use a Sako Quad (
http://www.sako.fi/), which allows use of different barrels on same action, covering calibres .17mach2, .17HMR, .22LR, .22WMR It is not as useful as you might think! Only ever use .17HMR and a separate .22LR rifle as re-zero is a pain between barrel changes.
Legal limit air-rifles are an excellent starting point so long as you can get close enough for accurate shot placement. Some land just isn't like that.
Above all; Respect your quarry. People will tell you that the ranges above are too short- don't kid yourself. Get plenty of practice on targets, simulating the shooting positions and ranges you will be using. Do not risk maiming a living creature- your duty as a hunter is humane dispatch of quarry and gun safety.
Happy hunting!