Quick search and I found this:
Animal Welfare Act 2006 (Scotland) - Docking
As from 30 April 2007 it will be illegal to dock puppies' tails in Scotland (other than for therapeutic reasons) or to travel across borders to have them docked. Regulations pertaining to this law will be approved by April 2007. It is permitted to show docked dogs in Scotland.
Animal Welfare Act 2006 (England and Wales) - Docking
As from April 2007 it will be illegal to dock puppies' tails (other than for therapeutic reasons or if a breeder can submit evidence to a Veterinary Surgeon that the dog is of a specified type to be used for work, rescue,
armed forces, police, pest control).
Regulations pertaining to this law approved April 2007 by England and Wales separately. It will not be permissible for docked dogs to be exhibited at shows where the public pay an entrance fee.
After the dates on which the regulations on exemptions came into force, members of the public should report any breeders to their Local Authority/RSPCA whose litters' tails are known to have been removed
without the required certification.
Anyone flouting the law can be prosecuted and fined £20,000, possible imprisonment and be banned from keeping animals (which could mean that other animals in their care could also be confiscated.
No-one should buy a docked puppy without accompanying certification to prove that the dog has had its tail removed legally and it is intended as a working dog under the categories listed in each region's regulations. This Veterinary certificate will be proof that the dog has been docked legally and will be important in prosecution cases. The dog also has to be microchipped with associated certification.