Yes, for almost any house in Henlow. Only a dozen buildings are listed. There is no conservation area at all. The neighbours file plans at a steady rate. The tougher negotiation is with the ground, because the clay underneath moves.
Henlow has 12 listed buildings. One is Grade I, one is Grade II* and the other ten are Grade II. Listing covers the whole building, inside and out, so changing one of them needs listed building consent from Central Bedfordshire Council on top of any planning permission, and that applies to replacement windows as much as to a two-storey extension. The area has no conservation area and no scheduled monuments either. Unless the house you want is one of the twelve, the window frames are your own business.
Central Bedfordshire Council received 163 planning applications for the area between April 2024 and June 2026, 65 of them in the last twelve months. That is applications made, and it says nothing about how many were granted. It does show that altering a house here is ordinary behaviour. Henlow's favourite hobby is drawing its houses bigger.
The British Geological Survey puts Henlow at class 3 for shrink-swell ground across every part of the area. Shrink-swell means clay that swells when wet and shrinks when dry, and the movement can crack a foundation that was dug too shallow. For an extension, that usually means deeper footings, a structural engineer's view before the design is fixed, and some thought about nearby trees, whose roots draw moisture out of the clay. It is a design and cost question, and building control will expect the foundations to answer it. The planners will let you build out the back, and the clay will decide how far down you have to go first.
In practice, most Henlow houses that are not listed and not flats can take many rear extensions, loft conversions and outbuildings under permitted development, the national rights that allow certain work without a planning application, provided the size limits are met. Anything bigger, anything on a listed building and any change to a flat needs consent. Newer estates sometimes had those rights removed by condition when they were built, so it is worth asking Central Bedfordshire Council whether the specific house still has them while you are still at the viewing stage.
Henlow gives owners a lot of freedom to change their homes. A dozen listed buildings and a layer of moving clay are the only real limits, and the clay can be engineered around.