I was being somewhat misleading, because most cocker spaniel bites are relatively minor. Just counting reported numbers of bites, let alone only those bites that people went to hospital to have treated, isn't really a good indication of risk. Hangbag dogs can often be nervous and snappy, but it's unlikely that a single snap from a Yorkie would be formally reported as a dog attack.
Does your cousin know why German Shepherds are the most expensive dog to insure with 3rd party injury cover? It doesn't necessarily reflect how common it is for dogs of that breed to bite people. It might be a matter of how much damage is done - would you rather be attacked once by a German Shepherd or twice by Yorkies?
I don't have a link, as I read it on paper a few years back. Looking online just gets USA figures, although I found one unsubstantiated statement that cocker spaniels and german shepherds were joint top biters in the UK.
Cocker spaniels came in 5th in the USA in a recent study on biting. Dachshunds were top.
There aren't any good stats, as far as I can tell. They don't even take into account how common the breed is, which is obviously a major factor in how many people are bitten by dogs of that breed.