Mostly yes, with paperwork. Every listed building here is Grade II. The old core of the village is a conservation area. The neighbours send in planning applications all the time. The clay underneath needs a say as well.
West Horsley has 27 listed buildings, and all 27 are Grade II. None are Grade I and none are Grade II*. Listing covers the whole building, inside and out, so almost any change that affects its character needs listed building consent from Guildford Borough Council as well as any planning permission, and that includes swapping windows and taking out internal walls. The numbers are small. In a village of mainly post-war and inter-war houses, most buyers will never own one, but those who do will need the council's agreement for most changes.
There is one conservation area, named West Horsley after the village. Inside it, the council looks harder at changes that alter how a house looks from the street, and some work that would be routine elsewhere needs permission. Check on the council's map whether the house falls inside the boundary, because the line can split a lane in two. The village Helen Allingham painted, with its thatched cottage, children and path, is the look the boundary exists to keep.
People do extend here, and often. The planning register logged 678 applications between April 2024 and June 2026, and 302 of them came in during the last twelve months of that period. Those figures show how many people applied. They say nothing about how many were approved. Someone played cricket in the park here in 1636. The village's main hobby now is the planning application.
The ground needs its own planning. The British Geological Survey puts the area's shrink-swell hazard at class 3, and every part of the area reaches that class. That means clay that swells when wet and shrinks when dry. It is a well-understood problem with standard solutions. Extensions on this kind of ground usually need deeper foundations, sometimes a structural engineer's design, and careful thought about nearby trees, whose roots dry the clay out. Budget for the engineer's report early, because building control will ask for one and the clay was here long before the house.
In practice, a house that is neither listed nor in the conservation area can often add a modest rear extension or a loft conversion under permitted development, the national rules that allow some work without a full application. Anything larger, anything at the front, and anything on a listed building or inside the conservation area means talking to Guildford Borough Council first. A lawful development certificate from the council, confirming the work is allowed, costs less than an argument afterwards.
Your freedom to extend a house in West Horsley is middling. Most houses can grow without much trouble, but the listed buildings, the conservation area and the clay all add steps along the way.