thank you for the clarification. based upon what you say, you would need to consider an application to the High Court for wrongful retention of goods together with costs. Providing you have unequivocal evidence of ownership of your dog, the first step in this regard would be to serve a written notice upon the individual that is keeping your dog of a demand for its return within say seven or 14 days warning that if the dog is not returned, you will commence proceedings in the High Court for wrongful retention of goods together with an order for costs against them.
if they ignore you, then you can make a claim using the following form under the torts ( interference with goods) Act for wrongful retention of your property and in order that your dog is returned to you. It is also worth making a secondary claim for what is known as " conversion" whereby you ask the court in the event that your dog has been sold in good faith ( both what you say this does not apply) by the person that has got your dog, but instead, the court orders damages to be paid to you in lieu of its return. As above, this should not apply but it is useful to include as a secondary provision in case your dog has been sold at the point you make the application and it cannot be returned.
The application can be made on form N208 and it must be sent to the High Court together with a fee of £528. you can apply for costs against the person holding your dog if you are successful. You will need to include some evidence that the individual has your dog be it an acknowledgement from them or some other form of photographic evidence or you mentioned that there is documentation with the police.
If the court is satisfied you both own the dog and that the person you apply against is holding your dog, the court will make an order that it is returned.