Yes, but in Highgate an extension usually needs permission from a planning officer, and sometimes from more than one consent regime. The area has hundreds of listed buildings. It has four conservation areas. Every postcode sits on clay that moves. Plenty of people still apply, and an extension here takes more paperwork and a longer wait than most.
There are 355 listed buildings in and around Highgate. Seven are Grade I, 31 are Grade II* and 317 are Grade II. Listing covers the whole building, inside and out, and any work that changes its character, from a new window to taking out an internal wall, needs listed building consent on top of ordinary planning permission. Carrying out the work without consent is a criminal offence. When the particulars describe a home in Highgate as full of "original features", they often mean features the law does not allow anyone to remove.
Four conservation areas fall within the same frame: Highgate Village, Holly Lodge Estate, Dartmouth Park and South Hill Park. Inside them, the council controls what happens to the look of a street as well as to individual buildings. Demolition needs consent, trees are protected, and work that would pass without a planning application elsewhere can need one here. Changes to the front of a house, such as windows, doors, boundary walls and roofs, get the closest attention.
The area also has one scheduled monument, the strictest level of heritage protection. That matters only to the few plots near it, where groundwork can need separate consent.
None of this has stopped people trying. The councils covering Highgate received 1,772 planning applications between April 2024 and June 2026, and 758 of them in the last twelve months. The applications are a record of what was asked for, and there is no record here of how many were approved. Searching the council's planning register for the street a buyer is looking at, to see what the neighbours applied for and how it went, is the most useful hour of research anyone can do before planning an extension here.
The British Geological Survey puts the area's shrink-swell hazard at class 3, and all of Highgate reaches that class. Shrink-swell clay swells when it is wet and shrinks when it dries out, so foundations have to go deeper than they would on firmer ground, particularly near trees. The ridge running from Hampstead to Highgate rests on a band of London Clay, and so does every rear extension built on this side of the Heath. A structural engineer should look at the plans before a builder prices them.
Seven of the listed buildings in the area are on Historic England's Heritage at Risk register. These are buildings in poor condition, and their repair can attract grant funding and will certainly attract scrutiny. For the owner of an ordinary house nearby, they explain why the planners in Highgate pay such close attention to anything old.
In practice, the permitted development rights that let homeowners elsewhere build a modest extension without applying count for little here. Flats have no permitted development rights at all, listed buildings need consent for almost everything, and conservation areas narrow what remains. The bishop once kept a toll-house on the road into Highgate to control what came up the hill, and the planning system now does a similar job for what goes on the back of a house.
The freedom to extend a house in Highgate is limited. A larger kitchen is possible, but planning officers, conservation officers and the clay all get a say before it is built.