Jez, per the wiki, addr:city is the postal city, which is Hove.

That looks better now, thanks: the building footprint is showing up.

This changeset includes a change to Sports Direct that makes it disappear from the map. Building parts need to be enclosed in a building. Do you know how to fix it, please?

Winton Cottages in Rottingdean have been similarly changed, incorrectly.

Philip,
I've reverted your change to Meadow Cottages in Woodingdean. They already have addr:substreet and addr:parentstreet: they should not also have addr:street added.

Yes, the document below makes it clear that "addr:city" is postal city, and addr:suburb is next lower tag that covers suburbs, villages, hamlets, etc.

osm.wiki/Addresses_in_the_United_Kingdom

Please be careful with streets here: Deborah Terrace is the substreet, not street.

You can also see UPRNs for buildings that no longer exist, so you have to be careful to avoid these. For example, in Peacehaven, plenty of single houses on a plot have been demolished and two put in its place. The UPRN tool may well show 3 UPRNs in this case, so I check the centroids to determine the correct UPRN. In some cases, the centroid seems a little off, but then I find that the outline needs adjusting from the aerial imagery; someone might have just plonked a rectangle there in the first place.

Using Rob's visualisation of the Open UPRN data: https://osm.mathmos.net/addresses/uprn/

It's rather manual, though. I have Rob's tools open in one tab and iD editor in the other, and copy across UPRNs where there is a single UPRN for a building and the centroid exactly matches. I always find on a survey that some buildings haven't been split yet, so I use StreetComplete to make the house number something like "7,9" and edit the outlines later. The UPRN tool found some places where I'd forgotten the "later" bit :-)

I've been waiting 24 hours for updates in F4 Map after 3D changes. Looks like I need to install JOSM!

Was the tower on the eye hospital supposed to be 8 metres high? It's been set to 80 metres, and the other one to 20 metres?