Moss m8, have a word with some of the farmers you pass in the mornings, i reckon if you approach properly and ask nicely they'll give you permission to shoot on their land.
now if your running a decent rifle anywhere from about 10-11.9ft lbs you should be good for rabbits, tree rats (greys only) and other vermin, mags, pigeon and rats. the cotton tails and tree rats are quite edible as is the pigeon

get yourself over to some air rifle forums and have an ask on there and they'll have all the info you need, pigeonwatch is a good one
also, i understand many people see the taking of any life to be abhorrent, i respect this view, i just have a different one.
remember people, meat is murder....tasty, tasty murder..

pete