Roland Perry wrote:

Town Hall, 128-142 High Road, Ilford, Essex, IG1 1DD

Yes, but it's still the address of the London Borough of Redbridge.

Which is in Essex.

Letters addressed to:

Town Hall, 128-142 High Road, Ilford, IG1 1DD
Town Hall, 128-142 High Road, Ilford, Redbridge, IG1 1DD
Town Hall, 128-142 High Road, Ilford, London, IG1 1DD
Town Hall, 128-142 High Road, Ilford, Redbridge, London, IG1 1DD
Town Hall, 128-142 High Road, Ilford, London Borough of Redbridge, IG1 1DD
Town Hall, 128-142 High Road, Ilford, Nevernever Land, IG1 1DD

....will all get to the same place. (For some reason a lot of my eBay traffic
has come from Richmond-upon-Thames and I've sent to customer supplied
addresses for "Surrey", "London" and "[no county entry]". All have arrived
at the same rate.)

It's true that Post-towns for an address may not be in the same county as
the address - for example, some villages in Bucks have "Henley" (Oxon) as
the post town, but the village is still in Bucks.

Yes because of where the mail goes via. But the Royal Mail dropped the
requirement for the county to be included back in 1996 when they switched
over their systems, and they're fine whether you use the administrative
county, the traditional county, the ceremonial county, the postal county, a
made up county or nothing at all.

There is a strange situation in Surrey I think in that some of their
administrative offices are not in the region that they administer (ie
Kingston).

Some of Surrey's County Council offices are in the Borough Of Kingston, an
area they no longer administer.

A hangover from the creation of Greater London. There seem to have been
umpteen schemes over the years for relocating to Woking but nothing ever
seems to come of them.