In the UK there are 4 breeds of dog that it is illegal to own (Pit Bull Terrier, Japanese Tosa, Dogo Argentino, Fila Brasileiro). The government says "A police or council dog expert will judge what type of dog you have" and "Going to court - It’s your responsibility to prove your dog is not a banned type" but no information is given about the form that this determination will take.

There is currently an example of this happening, where the breed was determined to be American Bully XL (a legal breed which is a derivative of and is physically similar to the illegal Pit Bull Terrier).

In this day and age the most obvious solution for defining a breed is some form of genetic testing, probably with some machine learning thrown in. In this case I would expect the rules to be well known, and hopefully published in a peer reviewed journal, and I am not aware this is the case. Another way would a be predefined list of physical traits that could be used to define a breed, but again this could be published and made available to people who were concerned and no such list is on the government page above.

How are illegal breeds of dog legally defined or determined?

  • The BBC TV news did mention "genetic test" but their online story only says "Tests have confirmed the dog was a legal breed". Mar 28, 2022 at 14:12
  • Note that "illegal bread" just means "the government is of the opinion that all dogs of these four breeds are dangerous". But owning a dangerous dog is illegal. Just with other breeds, that might depend on training. Some breeds can play nicely with your children if raised well, but are an active danger if trained for fighting. Or just if they are put into a different environment they don't know, owned by someone without a clue how to keep them under control.
    – gnasher729
    Mar 29, 2022 at 11:25
  • Now an American Bully XL is 90 to 150 pound. More muscle than you have. Much stronger than you are. Much stronger teeth than you have. You are not going to stop it. You really must know how to handle it.
    – gnasher729
    Mar 29, 2022 at 11:30
  • That law is weird. I have not heard of those dog breeds except the pitbull. Rottweilers and dobermans are just as dangerous as a pitbul and not on the list.
    – Neil Meyer
    Apr 4, 2022 at 16:50
  • @gnasher729 you wont stop a 66 pound dog that attacks you.
    – Neil Meyer
    Apr 4, 2022 at 16:52

1 Answer 1


Normally, initial identification is conducted by a police Dog Legislation Officer:

...or an officer trained in dog-related legislation with a good knowledge of the identification of the prohibited types of dogs.

Who will normally:

provide an expedited streamlined forensic report on the dog type and will almost certainly be the prosecution expert witness. Where the police are not the prosecution’s expert witness, they will identify an expert witness from a suitable organisation...

One such organisation is the British Veterinary Association, but other expert witnesses with the requisite knowledge and understanding are available.

Where the defence challenge the identification / type of dog:

the court may direct the experts to serve a statement on what they agree and what they do not agree

Although DNA testing is possible, in my experience the identification is based around the dog's appearance and physical characteristics.

For example, Annex 2 of this Guide(pdf) gives a starting point for identifying Pit Bull Terrier (PBT) types.

  • 1
    Stepping back a step, it is basically a question of fact for the court to decide based upon testimony including expert testimony and isn't necessarily defined further by law.
    – ohwilleke
    Mar 29, 2022 at 22:32

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