These sites may help:
Dog and Cat Bites | Health | Patient.co.uk
The above site is in regards to caring for the bite and aftercare.
https://sites.google.com/site/fidoin...g-a-dog-attack
This site pertains to laws and regulations and possible repercussions to the owner following a dog bite.
If the dog truly is in training, there is probably not a lot which will be done
A) due to the size of the dog
B) because dog bites are not considered extremely harmful to adults in the UK compared to cat bites and in general
C) because the owner is taking steps to reduce or eliminate the behavior
Anyway, that's my conclusion based on the site above. You may come to different conclusions following referral to the police assuming you have gone down that route.
Good luck!