Usually yes, and half the village seems to be doing it already. Listed buildings are few. Four conservation areas tighten the rules in places. Planning applications arrive by the hundred every year. The ground is the part that asks for the most care.
Chalfont St Peter has 27 listed buildings. None is Grade I, one is Grade II* and the other 26 are Grade II. Listing covers the whole building, inside and out, so almost any change that affects its character needs listed building consent on top of any planning permission. Twenty-seven buildings is a small share of a village this size, so for most buyers listing simply does not come up.
Four conservation areas fall within the area: North Park and Kingsway, Gold Hill East, The Firs Estate and Gerrards Cross Centenary. Inside them, the council takes a closer interest in demolition, trees, and changes visible from the street, and some extensions that would go ahead without an application elsewhere need one here. Search the house on Buckinghamshire Council's planning portal and conservation area maps to see whether it falls inside a boundary and what previous owners have already applied for. Two houses facing each other across a road can fall under different rules.
Buckinghamshire Council's records show 1,240 planning applications in the area between April 2024 and June 2026, and 556 in the most recent twelve months. Those figures cover applications made, which shows how much people want to change their homes here and nothing about how many succeed. A village that files 556 applications in a year treats the planning portal as part of the furniture.
The British Geological Survey puts the area's shrink-swell hazard at class 3, and every postcode in Chalfont St Peter reaches that class. Shrink-swell ground is clay that swells when wet and shrinks when dry, and trees and drought make the movement worse. For an extension it usually means deeper foundations and an early visit from a structural engineer, followed by a building control officer who wants to see the trial holes. The clay applies the same rule to every house in the village, however much the house cost.
On an unlisted house outside a conservation area, many rear extensions, loft conversions and outbuildings can go ahead under permitted development rights, within size limits, without a full application. Inside a conservation area those rights are narrower, and on a listed building almost any change needs consent. Anything that goes beyond permitted development needs a planning application, and a certificate of lawful development is the cheap way to confirm a project counts as permitted before the builders arrive. In a village of detached houses on decent plots, most of the arguing is over size, not whether the work can happen at all.
Your freedom to extend here is middling: most unlisted houses outside the four conservation areas have room to grow, while the listed and protected minority, plus clay under every postcode, keep the process slower and dearer than the plot size suggests.