Not really fair to keep just one -- they are social animals and you ought to have at least two or three -- so that's perhaps an acre of grass year-round.
As with any animal, you also need to be prepared for the time commitment, as well as organising winter hay, shelter, vet bills etc (traditionally the main occupation of lowland-type sheep is dying unexpectedly).
If in the UK you will need to register with DEFRA as a sheep keeper. You'll get a flock mark (a registration number) and probably an agricultural holding number too. You'll also need to make yourself very familiar with a host of special rules and regulations, such as what ear tags they must have and legal methods and frequency of movement. DEFRA will send you all the info. Lucky for you it's not quite as complex as keeping cattle, as I know well.
By the way, after the FMD scandal, taking sheep, goats or cattle "for a walk" on public land in the UK is now illegal. You can get a special licence for pigs -- don't know why. Llamas are OK.
If you want chops, the best thing is to have ewes and rear lambs, borrowing a ram as necessary for tupping. Conveniently, lambs change from lovely fluffy bouncy things into rather irritating adolescent thugs just exactly at the time when they are juiciest (autumn). Take care not to let them get fat, especially if not breeding.
Go for a light breed -- they eat less and are much hardier, though you will need better fences. Mountain breeds, Soay, Hebridean, Portland etc.
If you have more than 0.2 hectares of "farmland" (about half an acre), you can register your land as a farm holding and claim Single Farm Payment -- an annual amount which will eventually be about �200/ha. This applies to llamas, goats, horses etc too, but it must be done before 2005.