whats the law for owning american bulldogs?? (in the uk)

i met one out for a walk today without a muzzle, and with a girl, she must have been 16/17.
It was obviously viscous it was lunging for my PYR snarling and barking.
why do people let unexperienced dog owners have a dangerous breed. - its beyond me!

jackie spencer
London Uk

Money :(