Usually yes, but in many parts of the area the council gets a say first. More than 150 buildings are listed. Seven conservation areas lie within the wider area. The ground is clay that moves with the weather. Plenty of people extend here, but few of them get to skip the paperwork.
Historic England lists 158 buildings in the area: 3 at Grade I, 8 at Grade II* and 147 at Grade II. Listing covers the whole building, inside as well as out, so replacing windows, removing a wall or adding a rear extension usually needs listed building consent on top of any planning permission. Grade II is the most common tier and the one most buyers end up living with. It still means someone at the council will take an interest in your glazing bars.
There are 7 conservation areas within the wider area: Bletchingley, Merstham Village, Pendell, Place Farm and Brewer Street in Bletchingley, Rockshaw Road in Merstham, South Park, and The Green in Godstone. Inside one, alterations that would go through quietly elsewhere can need consent, and the council will judge the design against the character of the street as well as its size. You're designing for the conservation officer as well as for yourself.
The area also contains 8 scheduled monuments, the strictest tier of heritage protection. They mostly matter if your land sits on or next to one, and in that case the conversation gets a lot slower.
The neighbours aren't put off. Across the area, 1,795 planning applications were lodged between April 2024 and June 2026, and 776 of them in the most recent twelve months. That's live evidence that people here do alter their homes and are willing to fill in the forms to do it. Applying clearly isn't something only a stubborn few attempt.
The British Geological Survey puts the area in class 3 for shrink-swell clay, and about 99% of the area reaches that class. It's a published hazard classification: clay subsoil swells when wet and shrinks when dry. For an extension, that usually means deeper foundations, more care near trees, and a structural engineer's view before the builder quotes. None of that should stop the project. It just belongs in the budget from the start, before anyone assumes a shallow slab will do.
In practice, an unlisted house outside a conservation area can often use permitted development rights for modest changes without a full application. Once the house is listed, in a conservation area, or inside the Surrey Hills Area of Outstanding Natural Beauty, which covers about 7% of the area, assume you'll need consent and check with Tandridge before drawing anything. Asking before you buy costs an email. Asking after you've knocked through costs a lot more.
Your freedom to extend here is limited. It's workable on an ordinary house on an ordinary street, but heritage protections and the clay underneath make it slower, more expensive and more supervised than most buyers expect.