The British Isles (Great Britain, Ireland, and 6,000+ smaller islands) lie in the North Atlantic Ocean, off NW Europe.
They are north of the Tropic of Cancer (23.5°N), firmly in the Northern Hemisphere. London (51.5°N) is farther north than Calgary, Montreal, or Ulaanbaatar. The Gulf Stream/North Atlantic Drift moderates the climate, making it milder than latitude suggests.