He doesn't only travel in the UK. He has visited many parts of Earth, including (in no particular order):
- Australia ("The Enemy of the World"),
- Italy ("The Vampires of Venice", "City of Death", "The Masque of Mandragora"),
- China ("Marco Polo"),
- Antarctica ("The Seeds of Doom"),
- France ("City of Death"),
- Scandinavia ("The Girl Who Died"),
- The Levant ("The Crusade"),
- USA ("Daleks in Manhattan"/"Evolution of the Daleks", "The Impossible Astronaut"/"Day of the Moon", "Doctor Who" the TV movie, & many others),
- Mexico ("The Aztecs") ...
This list is far from complete &, if novels, audios & comics are taken into account, it could be extended almost indefinitely. The Doctor has also visited many places away from Earth -- the Moon, other planets, other galaxies, even other universes.
UK locations do show up disproportionately often, of course. Doctor Who is a British show, after all.