You can, though in Twickenham an extension comes with a lot of paperwork. Hundreds of buildings are listed. Dozens of conservation areas cover the map. The clay underneath has its own views. Yes, then, once the council, the clay and the conservation officer have each had their say.
Twickenham has 353 listed buildings. Twelve are Grade I, 50 are Grade II* and 291 are Grade II. Listing protects the whole building, inside and out, so on a listed house almost any change that affects its character needs listed building consent from the council. That includes new windows, a knocked-through wall and some of the things a buyer would class as decorating. Altering a listed building without consent is a criminal offence. On this map the rule that decides what you may do is the listing, and the purchase price comes second.
The bounding box around Twickenham contains 32 conservation areas, so the count takes in some across its edges as well as those inside it. Conservation area status protects the look of a whole street, not one house. It narrows what can be done without an application and brings closer scrutiny of roofs, frontages, materials and anything visible from the road. The council can also withdraw individual permitted development rights in particular areas. So check the council's conservation area maps for the exact address, along with any direction removing those rights, because two neighbouring streets can live under different rules.
One scheduled monument falls within the same box. That is the strictest tier of protection, and it matters mainly to anyone whose land adjoins it.
The neighbours are certainly building. The council's planning register holds 1,456 applications from April 2024 to July 2026, and 609 of them came in the most recent twelve months. The register can't tell you how many were approved. What it does show is that Twickenham extends all the time, and the drawings go to the council before the builders go to the house.
The British Geological Survey puts the whole area in shrink-swell class 3, so 100% of Twickenham reaches that class for clay that swells when wet and shrinks when dry. It is a published hazard class, and for an extension it changes the engineering more than the decision. Expect deeper foundations and a structural engineer's view, and plan for trees near the new walls to be part of that conversation. The fertile ground that grew Twickenham's market gardens before the railway came now produces foundation quotes.
Seven listed buildings in Twickenham are on Historic England's Heritage at Risk register. Their condition puts them under the closest scrutiny of all, and their repair may attract grant support. They are a problem for whoever owns them, not for the buyer of an ordinary house down the road.
In practice the house falls into one of three positions. An unlisted house outside a conservation area has the ordinary permitted development rights for modest rear and loft work, subject to the national limits. In a conservation area those rights shrink, and anything visible from the street usually needs an application. On a listed house, almost everything needs consent. With 32 conservation areas around it, many Twickenham buyers will find themselves in the second position, and a few hundred in the third.
Freedom to alter a home is poor in Twickenham. It is one of the most protected places on this site, and an extension takes patience, a good architect and a council that agrees.