To lawfully dock a dog’s tail, the vet needs to be satisfied that the dog will be used for legal shooting sports or other qualifying working life. It must also be done before the puppy is 5 days old. It must also be a spaniel, HPR (Hunt-Point-Retrieve) or a terrier, or a cross including one of those ( but only a pure-bred in Wales)
Here: Tail docking and the law
Tail docking was banned in 2007 in England and Wales, except under certain exemptions catered for in the Animal Welfare Act.
Puppies have to be docked before they are five days old.
This is before the neonate nervous system is fully developed and when bones are still soft.
Discuss your docking requirements with your vet well before the whelping date to avoid last-minute panics.
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.
Once the five-day time frame is up, the puppies cannot be docked.
Read more at https://www.shootinguk.co.uk/gundogs/health/tail-docking-key-facts-you-need-to-know-9672#k9qV54DQhQwT5dZ0.99
Well-intentioned legislation, it prevents unnecessary cosmetic bullshit like cropped ears and complete docking of big dogs like Rotties and Doberman Pinschers, but there are consequences to many working dogs who weren’t originally docked as per the requireents. .
I’ve seen first hand the damage an undocked tail can suffer, as not all dogs on shoots are docked because of the stringent legislation. The end of the tail can take days to heal, and on a busy day an undocked spaniel can look like it’s come from an abattoir.
If you can find a sympathetic vet to remove the damaged section of the tail as a preventative measure against future damage you’d be doing well by the dog, but given the legislation, unless you actually work him, you may just have to live with it and treat as necessary.