A Pitbull is legal in UK, as long as it registered with the Police, muzzled in public, kept on a lead in public, and has to be neutered. But finding one and obtaining one wont be easy. I would stick with just trying to get a Staff.
There are a lot of dog breeds that are cute as puppies so why do chavs all go for staffs now? Because they look hard. Sad really. You wouldn't see a chav walking a westie or a border collie because they 'look gay'.