For some reasons, I can't seem to add London, UK weather to my Viigo. Is it just me or Viigo?

Try just "london" (without the quotes). One of the choices returned is "London, United Kingdom (Westminster, England)". Not sure if that's the one you are looking for but to an overseas'er, it looks the most likely.

Wirelessly posted

Done that. Doesn't work. If after I select the location and add it, ir doesn't show up in my Viigo. It's only London, UK. Other cities work fine.