I've had a look for facts about tail-docking legislation. It is illegal in England and Wales, except for certain breeds, and totally banned in Scotland. "In England, the puppies must be one of the following listed breeds: HPR breed of any type or combination; spaniel of any type or combination of type; terriers of any type or combination of type.
However, in Wales, combinations of breeds (ie. cross breeds) cannot be docked, only the individual pure breeds. Furthermore, in Scotland, tail docking is completely banned, without exception"
and
"the vet will ask you to sign a statement declaring the dog whose tail is to be docked will be used for one of the following: a) law enforcement; b) activities of HM Armed Forces; c) emergency rescue; d) lawful pest control; e) the lawful shooting of animals." (and evidence shown) That is, dogs working in conditions where a luxuriant tail is likely to be in danger, much as long flowing hair is a danger to humans working near machinery.
The operation must be done within five days of birth before the nervous system is fully developed.
The legislation is at UK Tail Docking legislation as at May 2007
I've got another 'keen'... Ouch!