Great that you mention this. I noticed the layer a few times when going around checking history and all that.

Most of the time, when buildings were very recently added, I just left it as is (although like you say, offset is small), and sometimes when things are from way back in the days I tend to follow Bing.

I now went on and check out JOSM, and indeed, I have located the OSMUK cadastral parcels layer! Very helpful, thank you for letting me now and of course, happy mapping!