You can try, but in Holborn almost every alteration starts with someone else's permission. The district is packed with listed buildings. Conservation areas cover the streets between them. Even the clay underneath has a say. Holborn has been protected from change for so long that change now needs an application.
The wider area around Holborn holds 688 listed buildings: 41 at Grade I, 66 at Grade II* and 581 at Grade II. Listing covers the whole building, inside and out, so in a listed property new windows, a moved internal wall or a replaced staircase can all need listed building consent from Camden as well as, or instead of, ordinary planning permission. Work done without consent is a criminal offence, and the council can order it undone. In Holborn the original features are protected by law, and so are their owners' mistakes.
The same area takes in 15 conservation areas, among them Bloomsbury, Chancery Lane, Hatton Garden and Fleet Street. Inside a conservation area the council controls demolition and looks hard at anything that changes how a street looks from the pavement: roof extensions, new frontages, rear additions visible from the street, the materials used. A building can be unlisted and still sit under rules written for its neighbours.
There are also two scheduled monuments in the area, the strictest tier of protection, which matters only to anyone whose project gets close to one.
People clearly do still apply. Camden logged 320 planning applications in Holborn between April 2024 and June 2026, and 143 of them in the last twelve months. That's steady evidence that people keep asking to change things here. It says nothing about how many got what they asked for.
The ground has its own conditions. The British Geological Survey rates the whole of Holborn at class 3 for shrink-swell, its published measure of clay ground that swells when wet and shrinks as it dries. For an extension, a basement or even a large new tree near a wall, that means deeper foundations and a structural engineer's view early in the design. It's a routine cost of building here and no cause for alarm.
Six listed buildings in the area are on Historic England's Heritage at Risk register, which tracks protected buildings in poor condition. Those buildings attract grant interest and close attention from the conservation officers. A buyer of an ordinary flat down the road is unaffected, except that the officers handling those buildings may be the same ones reading their application.
In practice, permitted development, the national allowance for small works without a planning application, offers little help here. Most homes in Holborn are flats, and flats have far less permitted development than houses. On top of that, a listed building needs consent for most changes, and a conservation area narrows what is allowed without permission. A flat also comes with a lease, and the freeholder usually has to agree to alterations whatever the council says. Read the alterations clause in the lease and check the building's entry on Historic England's list before costing anything bigger than a kitchen, because between the council and the freeholder there are two parties who can say no.
Freedom to extend is about as poor here as anywhere in London. A buyer should assume the building is staying as it is.