On "Stop & Account” policing in the London Underground: http://www.newstatesman.com/blogs/staggers/2012/10/who-gets-asked-stop-and-account-and-why … Apparently the British Transport Police (@btp_uk) answer tweets
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