Edited sentence: The Phrase " North of Watford" came into use some time after the Bakerloo line opened up to Watford about 1918.The Phrase "North of Watford" comes from Londoners who looked at the London Underground map and if they wanted a day out would say "Lets go to Watford, the most northerly place" Londoners, just was not interested what was beyond Watford as they saw it was more than a day out