I'm not sure I believe the 1941 story. It was only two digits, so not what we would call a "postcode" today.
Simple postal numbers and references for towns and districts were around long before.
London EC, Birmingham 4, etc.
edited
"Hill produced an almost perfectly circular area of 12 miles (19 km) radius from the central post office at
St. Martin's Le Grand, near
St Paul's Cathedral in central London.
[3] As originally devised, it extended from
Waltham Cross in the north to
Carshalton in the south and from
Romford in the east to
Sunbury in the west — six counties at the time if including the
City of London.
[2] Within the district it was divided into two central areas and eight
compass points which operated much like separate
post towns.
Each was constituted "London" with a suffix (EC, WC, N, NE, E, SE, S, SW, W, and NW) indicating the area it covered; each had a separate head office.
[3] The system was introduced during 1857[1] and completed on 1 January 1858."
"In
1917, as a wartime measure to improve efficiency, the districts were further subdivided with a number applied to each sub-district.
[1] This was achieved by designating a sub-area served most conveniently by the head office in each district "1" and then allocating the rest alphabetically by the name of the location of each delivery office.
[1] Exceptionally and esoterically,
W2 and
SW11 are also 'head districts'."
https://en.wikipedia.org/wiki/London_postal_district#Origins
