Please do add some commentary!

While INSPIRE IDs do strictly speaking apply to the whole extent of the property, the same could be said to of the UPRN and even the postal address.

Where there is only one addressable building within an INSPIRE polygon (a single freehold property) and only a single UPRN, then I feel that in those cases the building can stand as a proxy for the whole property.

I'm not committed to including INSPIRE IDs, but if there isn't strong opposition I'd be inclined to include them as the link between INSPIRE ID, UPRN and postal address is something for which HM Land Registry charges a £20k/year subscription.