Which "place" fields we use
In Form:Person, "United Kingdom" goes in the "Nation" field.
Each of the four constituent countries goes in the previous field - that's what "UK Country" means.
The "County" field should ideally contain the current council area, as named on Wikipedia, e.g. North Ayrshire, County Down, Bristol, West Sussex, Greater London - but not the 30-odd London boroughs. However, locations of events in or before the 20th century generally used the traditional counties, e.g. Ayrshire or Sussex, and it may be impossible to tell the current council area, particularly if the only information is from a census. Therefore we accept the traditional counties in that field too.
Hamlets, villages, parishes, and London Boroughs (if no more specific locality is known) go in the "Locality" field.
The above is open to discussion!