In message , Peter Masson
writes

There is also a good practical reason for including the unnecessary
county in a postal address. Letters addressed to
CHISLEHURST
BR7 5xx
have not infrequently arrived late with a spurious Bristol postmark.
This does't seem to happen when they are addressed
CHISLEHURST Kent
BR7 5xx

There are also cases where two post towns in different parts of the
country share a name (Ashford, Richmond, etc). While the correct
postcode does differentiate, inclusion of the county name does reduce
the risk of misrouting.

Bearing in mind that the routing is done electronically by 'outbound
postcode' only, ie. the first portion, BR7 in your example, I fail to
see how adding the county can have any effect on this at all as it's
not even read by the system.

If the electronic reader fails to register the postcode (especially if
the address is handwritten) and the item is rejected for manual
sorting, it is only too easy for the Mk1 human eyeball to misread BR7
5xx as Bristol.

The Mk1 eyeball can't differentiate between an S and an R?

It needs replacing with a less defective version then.
--
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