It's either from Charing X (the actual Charing X, not the railway station) or from the Bank of England. It's just a rule of thumb, and doesn't really work some of the time.
i know its the actual x not the station, didn't know about the bank of england, but i will stick to my story that the street numbers in london make no sense at all, and that i love grid plans where building numbers are their coordinates. as in 1950 16th St, Denver, CO is 19.5 blocks west, and 16 blocks north of 0,0 (Broadway and Elsworth in this case)
i know its the actual x not the station, didn't know about the bank of england, but i will stick to my story that the street numbers in london make no sense at all, and that i love grid plans where building numbers are their coordinates. as in 1950 16th St, Denver, CO is 19.5 blocks west, and 16 blocks north of 0,0 (Broadway and Elsworth in this case)