Yes, outside the old core, and with more paperwork inside it. The village has three dozen listed buildings. One conservation area wraps the historic centre. Hundreds of planning applications go in every year. Thorpe extends its houses all the time, and it fills in a form first.
Historic England lists 36 buildings in and around Thorpe, three at Grade II* and 33 at Grade II, with none at Grade I. Listing covers the whole building, inside and out, so changes to a listed home need listed building consent from Runnymede Borough Council on top of any planning permission, and that includes work that would be routine elsewhere, such as new windows or a knocked-through wall. Thirty-six is a small number for a parish with a Domesday entry and a church on Roman foundations, but each of them comes with its own file.
There is one conservation area, named Thorpe, and it covers the village centre, where much of the building stock predates 1850. Inside a conservation area the council takes an interest in how a house looks from the street, and some of the extensions and alterations a homeowner could make without asking elsewhere need permission here. Ask the council's planning team for the conservation area boundary map and check which side of it a house falls on, because the line runs through the village and the two sides follow different rules.
People alter their homes here constantly. Runnymede's planning register holds 945 applications for the area around Thorpe between April 2024 and June 2026, and 406 of them came in the last twelve months. Not all of those are for houses, since the area includes a business park and the village's largest landowner is a theme park. Even so, a planning officer here will have seen the rear extension you have in mind several times already.
Outside the conservation area and away from the listed buildings, most of Thorpe's post-war houses, semis and bungalows sit under the national permitted development rules, which allow modest rear extensions, loft conversions and outbuildings without a full application, within size limits. With about one home in five a bungalow, the loft is the obvious place to look, and a roof-raise generally needs consent where a simple conversion may not. A lawful development certificate from the council costs less than an argument with a neighbour after the scaffolding goes up.
Freedom to extend in Thorpe is middling: easy enough across the post-war streets, and governed by a short list of old buildings and one tightly drawn historic centre. Most buyers will be fine, and the ones who are not will know which house they bought.