Mostly, yes. Across most of Purley, extending a house is ordinary suburban paperwork. There are a few dozen listed buildings and five conservation areas. Those are the streets where you should expect to wait longer. The neighbours are applying for planning permission at a steady rate, so extending is hardly unusual round here.
Purley has 34 listed buildings, of which 1 is Grade I, none is Grade II* and 33 are Grade II. Listing covers the inside of a building as well as the outside, so knocking through a wall needs listed building consent as well as any planning permission. With 34 listed buildings spread across a district of this size, the chance that the house you're viewing is one of them is small. If it is, the paperwork multiplies.
The five conservation areas are where most of the friction is: the Webb Estate, Kenley, Kenley Aerodrome, Bradmore Green and Upper Woodcote Village. Inside them, Croydon Council looks harder at anything visible from the street, such as roof alterations, side extensions, front walls and replacement windows, and some of the changes you could make without permission elsewhere need an application here. The Webb Estate is gated as well, so a builder's van has to get past the gate before it can even get to the planners.
There are 6 scheduled monuments in the area, the strictest tier of heritage protection. They matter mainly to anyone whose garden backs onto one.
Croydon Council's planning records show 1,183 applications in Purley between April 2024 and June 2026, 492 of them in the last twelve months. Not every one is an extension, but people here clearly do keep altering their homes, and the planners see a steady stream of applications from these streets. Search the address and the houses either side of it on the council's planning portal, because what next door was allowed to build is the best guide to what the council will let you do. The old Purley Council Offices were converted into flats in 2012, and plans to dig under the building for more flats were refused in 2015. Even the council's former headquarters couldn't get a basement approved.
Outside the conservation areas, most houses keep their permitted development rights, so a modest rear extension or a loft conversion within the national limits can often go ahead without a full planning application. Inside a conservation area some of those rights are reduced, and a listed building needs consent for almost anything. Flats don't get the same permitted development rights as houses, so a flat owner should expect to apply for nearly everything.
Freedom to extend in Purley is middling. It is easy on most streets and much harder in the five conservation areas and the 34 listed buildings, so check which kind of street the house is on before you plan anything.