Yes, you can extend a house in Hendon, provided it isn't one of the protected few. Most homes here are ordinary houses and flats with ordinary rules. A few dozen are listed. Four conservation areas add another layer. The clay underneath matters more than any of them.
Historic England lists 46 buildings in the area, none of them at grade I, two at grade II* and 44 at grade II. Changing a listed building, inside or out, needs listed building consent from the council on top of any planning permission, and that includes alterations that would normally be allowed without a full planning application. Grade II covers most listed buildings in England, so 44 of them make Hendon a place with some heritage. It's no museum.
Four conservation areas fall within the area: Hendon Church End, Hendon The Burroughs, Finchley Garden Village and Finchley College Farm. Inside them, Barnet's planners look harder at anything that changes how a house looks from the street, such as extensions, roof alterations, demolition and work to trees. Two of the four are named after Finchley, a reminder that conservation boundaries pay no attention to where Hendon thinks it ends. Barnet Council can tell you whether a particular house is inside one, and whether any of its usual building rights have been removed there.
The neighbours are certainly building. Barnet's planning register shows 1,045 applications from Hendon between April 2024 and June 2026, and 450 of them in the last twelve months. Whatever you have in mind, the planning department will have seen a similar application from somewhere in Hendon recently.
The ground needs more thought than the paperwork. The British Geological Survey puts Hendon in class 3 for shrink-swell, the hazard of clay that swells when wet and shrinks when dry, and every part of the area falls in that class. For an extension, that means deeper foundations, extra care near trees, and a structural engineer's view before the builder prices the job. Every house in Hendon is affected, so this goes into the budget wherever you buy.
One listed building in the area is on Historic England's Heritage at Risk register. That means a building in poor condition that might qualify for repair grants and will get careful attention from the planners. It has no bearing on extending an ordinary house nearby.
For most of Hendon, the usual rules apply. Houses outside the conservation areas and away from the listed buildings can often make modest extensions under permitted development, the building rights that don't need a full planning application, while larger schemes go through the normal application process. Flats are more restricted, since most external changes to a flat need planning permission whatever the area.
Your freedom to extend in Hendon is middling. For most houses the clay is a bigger constraint than the heritage rules, while the 46 listed buildings and four conservation areas tighten things for the streets they cover.