[HPFGU-OTChatter] UK postcodes: The intrigue!

[GulPlum]

Tabouli wrote:

>While we're on the subject of UK addresses, something that has always 
>perplexed me is those double barrelled postcodes like BS23 3JL.  How do 
>they work?  I've figured out that the 2 letter code in the first bit is an 
>abbreviation of the county, but what's the rest?  Do they divide the 
>county up into bits and number them?  What's with the other bit then, the 
>suburb code?

British postcodes go down to a level of, on average, no more than half a 
dozen residential properties, or a single commercial building. In other 
words, a house number and postcode is enough to identify any given property 
(for instance, the police recommend that people use special "invisible" 
inks to identify their valuables by including that minimum information.)

Even most British people don't have a clue how their postcodes work, so 
here's a quick rundown even for their benefit.

The format is:

LETTER (or two letters) NUMBER (which can be more than one digit) SPACE 
NUMBER (single-digit) LETTER LETTER.

Let's take my previous postcode: SW15 9BJ (I'm not stupid enough to give my 
current one in a public forum). :-)

SW is London South West. London also has E, N, NW, SE and W (see the 
compass points?), there is also EC (East Central), although there is no C; 
S and  NE don't exist either.

London is unique in that the name of the town itself isn't the basis of the 
postcode. The usual routine is that the first letter (or two letters) are 
an abbreviation for the town (or, in rural areas, the nearest large town). 
Bigger towns usually get a single letter (e.g. Birmingham: B; Manchester: 
M) and so smaller towns have to have two (Bristol: BS; Blackburn: BL, etc, 
etc.).

15 (fifteen, not one-five) is a district of of London South West. Because 
this is England, there's not a lot of sense to the way the numbers are 
allocated, as W6 was around one corner, SW7 was around another and SW14 was 
the other side of SW6. SW13 was on the other side of Thames, and I don't 
have a clue where SW16 is. :-)  These numbers (both in London and other 
large cities) have historical connotations, and were in use well before the 
advent of the modern postcode in the sixties.

Then there's a space.

The number 9 following the space is allocated by the Post Office and 
generally identifies a street (but not necessarily). The number itself has 
no historical connotations.

BJ at the end identifies a group of houses, usually not more than five or 
six, sometimes a single one. The letters are meant to have some kind of 
rationale, but I've never been able to determine it (the house next door to 
my previous home was SW15 9BW).

Two Central London postcodes (SW and EC, because of the density of 
commercial properties) can include an extra letter after the first half of 
the code. Thus, for instance, the House of Commons is SW1A 0AA (the House 
of Lords is SW1A 0BB).

Large buildings may be allocated a single postcode, or even a range of 
codes. For instance, BBC television HQ has over 100 postcodes for the 
single building, all starting W14 XXX. Just for completeness, the 
Birmingham BBC HQ is B5 7SD. "B5" is south-west of the city centre (B1); B6 
is north and B4 is way out south-east. So, just like London, the district 
codes make no sense whatsoever. :-)

--
GulPlum AKA Richard, a mine of useless information