Badsey-Ellis, Antony (November 2008). "The Underground and the apostrophe"(PDF). Underground News. London Underground Railway Society. Archived from the original(PDF) on 4 March 2016. Retrieved 21 February 2014.
Badsey-Ellis, Antony (November 2008). "The Underground and the apostrophe"(PDF). Underground News. London Underground Railway Society. Archived from the original(PDF) on 4 March 2016. Retrieved 21 February 2014.