You can apply to extend in Bloomsbury, but expect a long wait and plenty of conditions before the answer is yes. Hundreds of buildings are listed. Most streets fall inside a conservation area. Almost every home is a flat, so you would be extending somebody's shared building, not your own house. On top of all that, the clay underneath means any new foundations need a proper engineer.
Historic England lists 910 buildings in the area: 32 at Grade I, 81 at Grade II* and 797 at Grade II. Listing protects the whole building, inside as well as out, so changes that would be routine elsewhere, such as moving a wall, replacing a window or taking out a fireplace, can need listed building consent from Camden Council as well as, or instead of, planning permission. The Bloomsbury Group rewrote a generation's rules from these squares. A modern owner of a listed townhouse here can't move a staircase without asking Camden first.
There are 20 conservation areas in and around the district, among them Bloomsbury, Charlotte Street, Denmark Street and Chancery Lane. A conservation area brings closer control of anything visible from the street, including demolition, roof alterations and the materials on a front elevation, and Camden will judge a proposal against the character it was designated to protect. Ask Camden for the building's planning history and listing entry early on, because what earlier owners were refused is the clearest preview of what you will be told.
One scheduled monument sits in the area. That is the strictest level of protection there is, and it matters only if your land is next to it.
Plenty of people still try. Camden's planning register shows 1,188 applications in the area between April 2024 and June 2026, and 495 in the last twelve months. Most of that will be offices, institutions and flats being refitted, but it shows that alterations here do happen, slowly and on paper. The paperwork is a local industry in its own right.
The ground adds its own condition. The British Geological Survey puts the whole area in shrink-swell class 3, a published hazard class for clay that swells when wet and shrinks when dry. In practice, any new foundation, even for a small rear extension, needs to go deeper than it would on stable ground, and a structural engineer should see the plans before the builder does. The trees in the garden squares won't help either.
Fourteen listed buildings in the area are on Historic England's Heritage at Risk register. That marks buildings in poor condition, whose repair may attract grant money and will certainly attract scrutiny. It doesn't make any ordinary flat nearby riskier to buy. It does show how closely the rest of the stock is watched.
The practical point is that permitted development, the right to build small extensions without applying, belongs to houses, and here it barely applies. With about 95% of homes being flats, most changes need planning permission. A listed building may need listed building consent on top, and a leaseholder will usually need the freeholder's consent too. Anyone who owns one of Bloomsbury's few whole houses is still likely to find the listing or the conservation area has taken those rights back.
Your freedom to extend or alter a home in Bloomsbury is poor, among the tightest anywhere. Buy what is already there and plan to love it as it is, because changing it means years of correspondence with Camden.