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Ridiculous that postcodes/uprns lookups are not open data (yet). hohum.

They are in the UK but you have to have some magic understanding of around 15 separate files. Seems to be purposefully difficult.

NL as well, but the source data has a couple of indirections before you get to the postcode.

It's doable, monthly updatable for free, but requires a bit of processing and understanding of the geo structures.