So why, with houses dated 1881, has, for instance, April Street off Shacklewell Lane and laid out after 1866, the abandoned NE and not E in its street sign? Well, locals did not like becoming east. In 1891 they were still petitioning the Post Office: the change to E was “affecting property prices” and “putting off new residents”. The headmaster of one local private school refused to drop NE from his address, lest E discourage parents form putting their children in his charge. The Hackney Borough sympathised, continuing to put NE in street signs until WW1.
WW1 changed many things. Men volunteered to fight in their thousands. When their enthusiasm and numbers waned, conscription, introduced in 1916, took more men away from jobs, many of which came to be done by women. These jobs included the sorting and delivery of letters. Knowledge and experience needed to do the work had left with the men as they went to war. In 1917, to assist the female workforce new to the work, each of the 9 postal districts was separated into sub-divisions, serially numbered. 1 was for the subdivision with the district head office. From 1 onwards, they were numbered according to alphabetical subdivision: E2 Bethnal Green, E5 Clapton, E9 Homerton, E17 Walthamstow; E8 for Hackney.
See The Postal Museum: postal museum.org @thepostalmuseum; moving into new London premises mid-2017.