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There don't seem to be any properties in that list that violate the rule? The rule is house name or number and postcode. In the cases above, there are no houses that conflict on names or numbers that I can see?

Visit [1] and try DE4 4HA - addresses include "1 Council Square Brassington, MATLOCK, DE4 4HA", "1 Pleasant Cottage Miners Hill, Brassington, MATLOCK, DE4 4HA" and "1 Windyridge Red Lion Hill, Brassington, MATLOCK, DE4 4HA"

Try HD7 4PD to get "1 Moles Head, Golcar, HUDDERSFIELD, HD7 4PD" and "1 Prospect Place, Golcar, HUDDERSFIELD, HD7 4PD"

Try HD4 6XA and see "1 Broad Lane, Thurstonland, HUDDERSFIELD, HD4 6XA", "1 Blake House Thurstonland, HUDDERSFIELD, HD4 6XA", "1 Clough Cottages Thurstonland, HUDDERSFIELD, HD4 6XA", "1-2 Clough Cottages Greenside Road, Thurstonland, HUDDERSFIELD, HD4 6XA"

And of course there's the other direction: EC1N 8QX covers a bunch of flats in the same building, so one postcode includes "Flat G.7, Ziggurat Building, 60-66 Saffron Hill, LONDON, EC1N 8QX" and "Flat 1.1, Ziggurat Building, 60-66 Saffron Hill, LONDON, EC1N 8QX" - in other words, multiple properties have the same number within the street, and the same latitude and longitude. Also the building "number" has a hyphen, the flat "number" has a dot and can have a letter, and the building has a name too.

[1] http://www.royalmail.com/postcode-finder/

This is not a full list of addresses, but there are two no 10s there, and obviously as the postcode covers a large area with many streets, there will be some duplicate numbers, and many houses don't even have a number or street, and if you start to include house names as numbers, you will have duplicate names there too. Many addresses are as simple as rose cottage, village, POST CODE, and there might be many 'rose cottages' in that postcode.

It would be nice if it was a unique identifier, but the uk postcode is not, even combined with part of an address like 10, or even 10 high street, sometimes the village is also required to narrow it down. This might have worked for you on a limited set of data, but the assumptions are not valid across the uk.

>Many addresses are as simple as rose cottage, village, POST CODE, and there might be many 'rose cottages' in that postcode. //

This seems unlikely. In a small village people know the other house names enough to avoid a collision - in England I've a feeling Parish Councils used to keep order in this regard.

This page suggests that Local Authories legislate (bylaws I guess) on the allowed names: http://www.housenameheritage.com/hnh_extras_officialviewlong....

Quoting that link:

>"The Local Authority will liaise with the Royal Mail to ensure there is no conflict with names of other properties in the same street or immediate area, before formally registering the name. If there is a problem, an alternative name must be submitted. In some cases, the Local Authority may explore the possibility of a house number being registered at this point, in addition to (or instead of) the new name. Once the change has been approved, the Local Authority will normally advise relevant bodies such as the emergency services. The same procedure applies for brand new properties which, for whatever reason, cannot be numbered (however, virtually all new properties today are numbered)." //

It may seem unlikely, but that's the way it works (see better examples in the michaelt post above). Often postcodes cover more than one village, and there are thus duplicate street numbers or names. Some attempt is made to avoid clashes for new addresses, but there are plenty of existing ones. You need more than a postcode and number to identify an address, sometimes a street and/or village is also required.

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