Yes, but Calne makes you ask nicely. Nearly two hundred buildings are listed. The old centre sits inside a conservation area. The clay underneath moves with the weather. Plenty of people extend here anyway, and the sensible ones budget for the paperwork and the foundations before the kitchen.
Historic England lists 194 buildings in and around Calne: 1 at grade I, 15 at grade II* and 178 at grade II. Listing covers the whole building, inside and out, so on a listed home almost any change that affects its character needs listed building consent on top of any planning permission, and that includes the jobs owners assume are routine, like replacing windows or knocking through a wall. Doing the work first and asking afterwards is not a shortcut. It is a criminal offence, and the new owner inherits the problem.
The area has 1 conservation area, covering the historic core of Calne. Inside it, demolition, some alterations to the front of a house and work to trees need extra consent, and the council can remove the usual permitted development rights for particular streets. If the house you like is in the conservation area, ask the council which rules apply to that address before you plan anything bigger than a paint colour, and even the paint colour is worth checking.
There are also 3 scheduled monuments in the area, the strictest protection tier of all. They matter mainly if the land you are buying sits next to one, because any work that touches them needs consent from the national heritage body, not the council.
The neighbours are not deterred. Between April 2024 and June 2026, Calne saw 372 planning applications, 172 of them in the last twelve months. That volume says homeowners here extend, convert and alter all the time. It says nothing about how many were approved, so treat it as proof that people try, not proof that everyone succeeds.
The ground needs as much thought as the heritage. The British Geological Survey places every postcode in Calne in shrink-swell class 3, a published hazard class for clay soil that swells when wet and shrinks when dry. For an extension, that means deeper foundations than a builder might quote from habit, a structural engineer's view before the drawings are final, and attention to trees near the new wall. It is a design consideration, not a reason to walk away, and the builder who waves it off is the one to walk away from.
Two listed buildings in the area sit on Historic England's Heritage at Risk register. That describes their condition: repair may attract grant support, and it will certainly attract scrutiny. It is not a hazard to the owner of an ordinary house down the road, although anyone buying one of those two buildings is buying a project with an audience.
In practice, most Calne homes sit outside the listed stock and the conservation area, and for those, a modest rear extension or loft conversion may fall under permitted development without a full application. Check that before you assume it, because the rules depend on the house type and on what has already been built. Anything listed, or inside the conservation area, starts from the assumption that you need consent and works outwards from there. The ground conditions apply either way.
Calne is a harder place than most to extend a home: heritage in the middle and clay underneath everywhere. The extension is usually possible, but the time and money go into getting permission and digging deep enough.