Most homes can be extended without much fuss. Sixteen properties carry Grade II listings. Two conservation areas cover parts of the village and the road into Bognor. The rest of the housing stock, which is the bulk of it, sits outside both. The freedom-to-extend question turns entirely on which side of those two lines your house sits on.
On listings, sixteen properties in the village are protected. All sit at Grade II, the standard level of statutory protection for buildings of special interest. None reach the Grade II-starred or Grade I level. If you own one of those sixteen, almost any change to the building requires listed-building consent in addition to whatever planning permission would otherwise apply. The consent process is its own animal: slower, more contested, and the council's heritage officer becomes the person whose opinion matters more than your architect's. The good news is that sixteen out of around two and a half thousand homes in the village is a small slice. The bad news, if you happen to own one of them, is that the slice you bought is the one with the conversation attached.
On conservation areas, there are two: the Aldwick Conservation Area covering the village core, and the Bognor Regis (Aldwick Road) Conservation Area covering the route into the town. Inside a conservation area, the rules around extensions and alterations are tighter than outside. The permitted-development rights normally available without a planning application are narrower than they are on a standard residential street. Changes to the visible elevation tend to face the most scrutiny. The brief flags no separate Article 4 directions on top of the baseline conservation framework, which suggests the standard conservation-area rules are doing the work here. None of this prevents extensions and alterations. It means the design will be reviewed by somebody whose job is to mind the streetscape.
In practical terms, if your home sits outside both the listed register and the two conservation areas, you have the standard set of permitted-development rights every homeowner gets: rear extensions, loft conversions, garden buildings, replacement windows, the lot, within the published limits and without a planning application. If your home is inside a conservation area, the same projects often need a planning application even when they would have been permitted elsewhere. If your home is on the listed register, almost anything substantive needs consent before you start, and the conversation is the project. The first category covers most of Aldwick. The second covers a meaningful minority. The third covers sixteen homes and is the slowest of the three.
Aldwick rates three out of five on freedom to extend, which is the score for a village where the heritage rules bite in two places and not in the rest. If you bought a post-war bungalow inland of Aldwick Road, the planning officer barely needs to know you exist. If you bought a Grade II property on the conservation map, the planning officer is now somebody you talk to as often as your neighbours.