Yes, mostly, but you'll meet committees if you're close to the water or living in something pre-Victorian. About 150 listed buildings sit inside the town footprint. The Westbourne conservation area covers the protected village to the east. Almost a fifth of the area falls inside the Chichester Harbour designated landscape. Newer houses well inland of the harbour have a quieter path through the planning system.
The brief counts 150 listed buildings inside the area. One is graded I, the highest level of statutory protection in England, reserved for buildings of exceptional national interest. Two more carry a grade II-star designation, the middle tier for particularly important examples. The remaining 147 are listed at grade II, the most common form of statutory protection, which covers most of the period stock that makes the town look the way it does. A listed-building consent is needed for any change that affects the character of a listed structure, inside or outside, which is planning shorthand for sympathetic materials and reversible work, not a tradesman with a power tool and a Monday morning. Owning a listed house does not stop you extending it. It stops you doing so cheaply, and it stops you doing so on the timeline you had in mind.
There is one conservation area inside the bounding box: Westbourne, the protected village out to the east. Conservation-area designation does not block extensions but tightens what can be done without formal consent, and raises the bar on what counts as acceptable in terms of materials and style. The brief does not catalogue every specific direction or restriction for the Westbourne area, so anyone buying inside the conservation boundary should pull the local planning authority's published documents before committing to a project. The wider picture also takes in the Chichester Harbour designated landscape, an Area of Outstanding Natural Beauty that overlaps about 18% of the local footprint and adds its own layer of consideration for any waterfront or near-waterfront alteration.
Outside the conservation envelope and outside the designated-landscape overlap, most properties keep their standard development freedoms, which is the planning shorthand for being able to do reasonable extensions and outbuildings without a full application in many cases. Inside the heritage envelopes, that default does not apply, and most work goes through the planning system the long way round. The brief logs roughly 239 planning applications across the area in the last twelve months, which is a steady level of activity rather than a frozen town. People are extending, altering, and building. They are doing it with paperwork.
Freedom to extend rates as average here, which is the honest middle of the spectrum. This is not the locked-down heritage village with grade I on every street, and it is not the post-war suburb with no constraints to speak of. If your house is listed, sits inside the Westbourne conservation area, or looks out at the harbour from the front step, expect a longer timeline than the kitchen-extension blog led you to believe. If your house is post-war, inland of the harbour, and the most ambitious thing about it is the conservatory, the planning system will mostly be a form-filling exercise rather than a multi-year conversation.