The only way you can legally dock terriers now is to take them to vets and prove that they are working dogs, they then do the job and give you a certificate. The only drawback is that you now cannot show a terrier in a puppy class with a docked tail even though you have the certificate. p
Personally I do not like terriers with undocked tails but we have to get used to it as it is illegal to dock unless as I said they are proved to be working.