Can I extend my house in BR7?

Assume the designation until you have checked the point

Much of central Chislehurst, including streets around the common, sits in a conservation area. Permitted development is narrower there, and roofscape and frontages are sensitive. Other BR7 roads are ordinary suburb and are decided as normal householder applications. The Green Belt lies to the south and east of the town. A house can be inside BR7 and outside every one of those designations.

The report’s constraint check is a point-and-nearby search of the national datasets, not a walk of the whole district. If it says a conservation area was not found at the point, that is about that point. If it says one was found 300 metres away, you are near the edge and the drawings will be looked at with that in mind.