You can extend a home in Pimlico in theory, and in practice you'll be asking permission at every step. There are 347 listed buildings in the patch. There are 19 conservation areas overlapping it. Most homes are flats inside somebody else's building. The extension you have in mind needs the council, the heritage rules and probably a freeholder to agree with you.
Historic England lists 347 buildings in the area: four at Grade I, 61 at Grade II* and 282 at Grade II. Listing covers the inside of a building as well as the outside, so in a listed house a new partition, a replaced window or a fireplace taken out can all need listed building consent, on top of any planning permission. That consent is a separate application, and the council can refuse it on grounds of history that an ordinary planning application never has to consider. The cornicing in a Grade II flat belongs, in a legal sense, a little to everyone.
The 19 conservation areas that overlap the patch include Pimlico itself, Churchill Gardens, Dolphin Square and Lillington Gardens. Inside a conservation area, changes that would be routine elsewhere, from demolition to work on the street-facing side of a house, tend to need the council's consent. Stucco fronts painted to match the rest of the terrace aren't a matter of local taste. They're the reason the designation exists.
People do try. Westminster logged 715 planning applications in Pimlico between April 2024 and June 2026, 362 of them in the last twelve months. That's a lot of residents filling in forms to change something. The brochure line "potential to extend, subject to consents" rarely mentions that the consents are most of the project.
The British Geological Survey puts shrink-swell clay in Pimlico at hazard class 3, and every postcode in the area reaches that level. That's a published geological class, and it means the ground moves as it wets and dries. For an extension or a basement, that points to deeper foundations and a structural engineer's report as a normal part of the budget. It's a reason to plan the foundations properly, and it shouldn't put anyone off.
Three listed buildings in the area are on Historic England's Heritage at Risk register. Those are buildings in poor condition whose repair may attract grant support and will certainly attract scrutiny. For the owner of an ordinary flat nearby they change nothing, apart from reminding everyone that the inspectors are paying attention.
The practical position follows from the housing. Most homes in Pimlico are flats, and flats carry none of the automatic householder rights to extend that a house elsewhere might use. A listed building or a conservation area narrows whatever room is left. Almost any change to the structure or the frontage here needs an application, and in a converted terrace the freeholder's consent under the lease as well. Look the building up on Historic England's list and read the lease's clause on alterations while the solicitor still has the paperwork open. Two buildings on the same square can face very different rules, depending on which side of a conservation area boundary they fall and whether either one is listed.
Freedom to alter a home is about as limited in Pimlico as it gets. If you need room to grow, buy the space you need now, because the stucco isn't going to stretch to fit you later.