You can extend a home in Fitzrovia, but almost every change needs permission first. More than a thousand buildings in and around the district are listed. There are 23 conservation areas. Very few homes are houses at all. You can expect to need consent for most changes, including the windows.
Historic England lists 1,133 buildings in and around Fitzrovia: 46 at Grade I, 124 at Grade II* and 963 at Grade II. Listing protects the whole building, inside as well as out, so a new wall, a replacement staircase or a different sash window can all need listed building consent as well as planning permission. Doing the work without consent is a criminal offence, and the council can make you undo it. Grade I is the top category nationally, and a building that would sit there has been judged among the most important in the country.
The wider box around the area includes 23 conservation areas, among them Charlotte Street, Charlotte Street West, Cleveland Street, Fitzroy Square and East Marylebone. In a conservation area, changes that would be routine on an ordinary street, such as new windows, a roof alteration or taking down a wall, can need the council's consent. When it decides, the council looks at the character of the street as well as the building itself. Since the boundary changes of 1900 moved half of Charlotte Place and parts of Charlotte Street and Rathbone Street from St Pancras into Marylebone, check which council covers the exact address and read that council's guidance on the street.
There are also 2 scheduled monuments in the same wider area. Scheduling is the strictest level of protection, and it matters mainly if a home stands close to one.
Plenty of people still make changes. Westminster and Camden councils received 766 planning applications in the area between April 2024 and June 2026, including 355 in the last twelve months. That shows the councils do receive a steady flow of plans here. It says nothing about how many of them were approved.
The British Geological Survey puts the whole area, 100% of it, in shrink-swell class 3 for its clay ground. Clay soils swell when wet and shrink when dry, so a rear extension or a basement needs foundations that allow for the movement. That means paying a structural engineer to look at the ground before an architect starts drawing. It is a reason to design carefully, and no reason to abandon the plan.
Historic England has 11 listed buildings in the area on its Heritage at Risk register. These are buildings in poor condition whose repair may qualify for grant funding and will be closely watched by the councils. They are a concern for their owners, not for someone buying a flat next door.
In practice, most homes here are flats, and flats do not have the automatic permitted development rights that houses get, so almost any external change goes through a planning application. A listed building adds a second consent on top. A flat on a lease usually also needs the freeholder's agreement. Plan on about three sets of approval for anything more ambitious than painting a wall.
Fitzrovia gives you very little freedom to extend or alter a home. The councils and the listing rules decide almost everything, so if you want to change a building substantially, buy somewhere else.