There is a register of exempted dogs which owners can apply to be added to. The dogs have to be neutered, chipped, tattooed and muzzled & on lead in public. It truly is a ridiculous system that dictates a dog be destroyed simply because of how it looks.
The ridiculous thing is that the legislation has done absolutely nothing to reduce the prevalence of pitbulls in the UK, if anything it made them more desirable to the type of people whose irresponsible dog ownership caused the knee-jerk reaction which spawned the ridiculous dangerous dogs act!
The other 3 breeds governed by the act are all molosser breeds - tosa, fila and dogo, all due to a very small number of irresponsible owners.