as our address format. Of course, you only *need* "20 AB1 2CD", but
the inclusion of the street and post town provide a useful "checksum"
to ensure the postcode is correct, and the street address probably
assists the postman on his walk as well.

We could feasibly go to "20 Anystreet AB1 2CD" and even remove the
post town, but without any kind of "checksum" I would imagine a lot
more post would end up in the wrong place.

I think one problem is that the concept of the post town isn't something
that has ever really been effectively communicated to the public at large as
it has always caused confusion when counties have been included in the
address. Presumably it may also not be immediately useful to postal
services other than the Royal Mail who might organise their network
differently. Without looking it up I couldn't actually tell you if the
county in the address file is the county the post town is in, or the county
the address is in, and even then the county can be debatable too. I think
it has always been in the wrong part of the address and that people should
have been encouraged to write addresses something like:

Name
Number Street (or building name etc)
Town (or village or whatever - NOT the post town).
County

BIT TO HELP OUT CARRIER

BIT TO HELP OUT CARRIER would be Post Town and Post Code if using Royal
Mail but could be potentially something completely different for other
carriers. So there is basically an address that the public at large would
understand that would also allow the carrier to deliver accurately if need
be, and a separate bit that is there to help make delivery more efficient.