Reiki is not a substitute for professional Veterinary Treatment.
"The Veterinary Surgery Act of 1966 prohibits anyone, other than a qualified veterinary surgeon from treating animals, including diagnosis of ailments and giving advice on such diagnosis"
However the healing of animals by contact, by the laying of hands or distant healing is legal. The Protection of Animals Act 1911 requires that if an animal clearly needs treatment from a veterinary surgeon the owner must obtain this.
Reiki is a non-medical therapy that compliments and supports all other healing therapies, including veterinary medicine, and is a valuable part of a combined approach to healing and health maintenance.