Rules-wise, growing veg for sale isn't a problem, as is small-scale egg production. Livestock is another matter - Defra rules are pretty strict. We raise sheep and pigs, and have to go through hoops to ensure that everything is as Defra says it should be. It's a lot of work, and probably not economical on just an acre.
Raising for home consumption, though similarly fraught with regulations, would be an option on that amount of land, however. And you have to manage the grass somehow, so if it's not to be ploughed or tilled, then you might as well run some stock on it. It's not cheap, though - either in terms of time or money.