Birthrights, a legal charity devoted to protecting human rights in childbirth, has published various factsheets, including one on the legal position on unassisted birth or free-birth. It lays out the legal position in England and Wales (presumably it also applies to the Scottish legal system).
All the factsheets can be accessed here: http://www.birthrights.org.uk/advice/factsheets/
(Also see the links section on the right side of this blog.)