The biggest reason they can go after any of the above groups is a Section 59 Anti Social Behaviour, which covers a wide range of offences, but the nicest bit being the permission to seize a vehicle constantly involved. Not so easy with non registered vehicles.

With regards to numberplates, ANPR etc, its all well and good if they are legitimately registered, genuine plates, and registered at the keepers genuine place, which isn't the case most of the time. Might explain why said "road legal" vehicles are chased, as they are flagged on the PNC, or set off the ANPR for no insurance etc.

Its a lovely idea that they can just be rounded up, but not a reality, and it takes a lot of resources which isn't always available.

There has been a nice clampdown in Bromley recently, so hopefully it will spread.