Weighing just 11 ounces and standing at four inches tall this is Tyson - believed to be Britain's smallest dog. miniature ten-week-old Tyson measures barely 4.5 inches tall and is barely a quarter of the size of his four brothers and sisters. his owner has been forced to build a special crate for the miniscule pup to live in, as his bigger siblings think he is just a TOY. Tyson was born on Mother's Day as part of the litter of five and is a Lhasa-Chi (a cross between a Lhasa Apso and a Chihuahua).