There is some analogy to be had here. (via @iamlei)pic.twitter.com/3tiP9C6rEo
You can add location information to your Tweets, such as your city or precise location, from the web and via third-party applications. You always have the option to delete your Tweet location history. Learn more
but before London of course.
Twitter may be over capacity or experiencing a momentary hiccup. Try again or visit Twitter Status for more information.