Land with valid planning permission is generally worth more than land without it, since it removes uncertainty and reduces the time and risk for a buyer wanting to build. The scale of the increase depends on the type of permission granted, local demand, and how long remains before the permission expires.
Planning permission typically adds value to a site because it removes a significant source of uncertainty for a buyer: the risk that permission might be refused, delayed, or granted with conditions that change the viability of a project. A site with a live, unimplemented permission for a house, for example, can usually command a higher price than equivalent zoned but unpermitted land, since a buyer can proceed to build with more confidence and a shorter timeline.
The scale of any uplift depends on several factors, including how closely the permitted development matches what a typical buyer wants to build, how much time remains before the permission expires (permissions generally last five years, after which they lapse unless extended), and local market demand for building land in that area. A highly specific or unusually conditioned permission may add less value than a more flexible one.
It's worth noting that planning permission attaches to the land itself, not the individual applicant, so a new owner generally benefits from an existing permission once they acquire the site, provided it hasn't lapsed and the development hasn't already commenced under different conditions.