Pitbulls are on the banned breeds list because they can just go from being friendly, placid dogs to attack mode in a split second with no warning, they also have locking jaws - once they're attached it's almost impossible to get them off again.
You can still keep them, but they must be on a leash and muzzled when out in public, neutered and have public liability Insurance, which costs about £70 per month, at the cheaper end of the scale. The Police have a 137 point "check list" to determine if a dog is or is not "dangerous" if it fails more than 50% of the points, it's dangerous, and can be put down if a Court so orders, which they almost invariably do.
Jack Russells can be feisty little sods too, some have a very strong "prey drive" and were originally bred to "go to ground" after Foxes and flush them out for the hunt - many hunts still have "terrier men" among their followers for this purpose.
Now, they're mainly used as rat catchers, if they're not just pets, and they're very good at it, even without formal training - my late one was an absolute demon for killing rats and squirrels - he'd even have a go at the local cats given the chance.
