"As cocker spaniels are not classed as a dangerous breed, I doubt they'd do much"
WRONG!!!!
The dog is at SERIOUS risk of being PTS at foot of a court order under the Dangerous Dogs Act and of course the OP is at risk of legal action too. He does not have to be a "banned" breed to suffer the punishment if he has bitten and there is no such thing as leniency for a one-off offence. What happens will depend on the bitten man's compassion for animals and whether there is police involvement.
It goes without saying that until you've addressed and resolved the problem 100% he should be kept away from your DD NOT because he is automatically a risk to her but because you don't yet know why he acted as he did.... and for that a vet's surgery is your first stop.
If your vet suggests that you have your dog euthanised, tell him to fuck off and get back to me, please. Most aren't that stupid but there's always one of course.
When you've checked him out with a vet, andif he can find nothing physiological, you have two options... work with a behaviouralist or approach a NO KILL rescue to take your dog on and rehabilitate him if you're not willing to do so yourself.
It must be remembered that there are some overbreeding and other problems with Cockers which have led them to suffer what's called "Cocker rage" - striking out for no apparent reason. (Only there is a reason, as I said, bad decisions on the part of breeders). This is an area which IMHO requires a behaviouralist employed by the owner or experienced assessment and rehabilitation by a good rescue.
I'm not even discussing having him killed, I don't consider that an option for ANY healthy dog, and I don't intend to get into debate about that issue on this thread. If people want to argue amongst themselves, fine, if they want to argue with me, put it on a seperate thread here or on the Doghouse and I'll give a bloody good defence of the dog when I have time... which isn't now.
All I will say is this - the dog was on a lead, changes in the home, hot day and some prat put his hand into the dog's face without asking the owner if he could stroke the dog... FFS! We teach our children not to do that, don't we?! Dickhead!
worried, you'd be wise to call your BIL very soon and see what action, if any, the man intends to take, what the extent of the injury is and what his attitude and demeanour was (apart from shock and pain of course). Then take it from there.
Right now I'd be considering moving the dog out of the home personally, so that if the authorities came to seize him he wasn't there but he was in safe, experienced and sensible hands. Again, that's not up for discussion here, it's my personal view and I must making the OP aware of the fact that it would not be a legitimate action... but would be in my opinion a moral one. I'm just offering advice and options.
PM me if there is anything I can do, worried.