Yes, but you'll be asking permission far more often than you'd like. Nearly three hundred buildings are listed. The historic core is a conservation area. The neighbours keep applying anyway. You can extend here. You just can't do it quickly or quietly.
Marlborough has 294 listed buildings. Two are Grade I, 11 are Grade II* and 281 are Grade II. Grade II covers the bulk of them, but Grade II still means listed building consent for any change that affects the building's character, inside or out, on top of whatever planning permission the work needs. Replacing sash windows, knocking through a wall, changing a roof material: on a listed house, all of these need consent. The town was last rebuilt in a hurry after the Great Fire of 1653. The listing system would prefer that remained the last time it happened.
There are two conservation areas, Marlborough and Manton. Inside them, the council has more say over what happens to an unlisted house too, especially anything visible from the street, and some work that would go ahead without an application elsewhere needs one here. Being unlisted doesn't take a house outside the conservation area.
The area also has five scheduled monuments, the strictest tier of protection, among them the Marlborough Mound. For most house buyers these matter only if the garden backs onto one.
None of this has stopped anyone trying. Between April 2024 and June 2026, 1,218 planning applications were lodged in the area, 539 of them in the twelve months to June 2026. Marlborough is clearly not a place where nobody alters their home. People do it all the time, with forms, drawings and patience.
What this means for a buyer comes down to which house they buy. A post-war house outside both conservation areas will have much the same permitted development rights as anywhere else, and a modest rear extension may need no application at all. A listed cottage in the middle of town needs consent for things most owners wouldn't think of as building work. Before offering on anything old, check the listing register and the conservation-area maps, and ask Wiltshire Council for pre-application advice if the extension is the reason you're buying.
Your freedom to change a home in Marlborough is limited, and it's the town's weakest point. It's manageable on the newer streets, slow and closely watched in the old centre, and anyone buying a period house for the project should budget time as well as money.