Oh I'm so glad you added that you know that this is not the "official" term, I guess some people here get upset when the term is used, but I only suggest people stay away from breeders who advertise "Teacups." London is so small for 10 weeks, and I really hate to see a puppy leave a breeder before 12 weeks especially a tiny. Most good breeders say 12 weeks and two pounds is the minimum. You have to watch out for hypoglycemia, and please teach to use stairs, not jumping off of beds or couches! Here's a link on toy breed hypoglycemia become familiar with the symptoms.
Toy Breed Hypoglycemia London is adorable!