For most houses in Nailsea, yes, you can extend, and the town makes it more straightforward than a lot of places. This is largely a post-war settlement, two in three homes are houses, and that ordinary stock comes with the usual permitted-development freedoms. Heritage protection is real here but concentrated. Around fifty listed buildings and a single conservation area sit mostly at the edges rather than across the everyday streets. Something like three hundred planning applications went in over the past year, so extending here is a well-trodden path rather than a fight.
The listed buildings are where the rules tighten. There are around fifty of them in and around the town, and only a handful carry the higher grades: two at the very top and two more a notch below. The large majority are grade two, the everyday tier of listing. If you own one, almost any change inside or out can need listed-building consent, from the windows to an internal wall, and the protection wraps the whole building rather than only the handsome front. The saving grace is that these homes are the exception. Most cluster in the old courts and churches on the fringes, such as the fifteenth-century Nailsea Court, rather than on the streets where most families actually live.
Nailsea has one conservation area, at Nailsea Kingshill. Inside its boundary the bar sits higher: alterations that would be waved through elsewhere can need extra consent, knocking things down is controlled, and even the trees get a say. There are also three scheduled monuments in the wider area, including remains of the old glassworks and colliery, though those are sites to build well clear of rather than homes anyone is renovating. For the overwhelming majority of Nailsea addresses, none of this applies at all.
In practical terms, that leaves most owners with plenty of room. An ordinary post-war house that is neither listed nor inside the conservation area can usually take a rear extension, a loft conversion or a garden room under permitted-development rights, with a full application reserved for anything larger or tight to a boundary. The steady stream of applications through the town shows the appetite is there and the permissions are gettable. The two questions that decide your freedom are blunt ones: is the house listed, and is it inside the Kingshill line. Answer no to both, and you are in comfortable territory.
So can you extend a house in Nailsea? For most of the town, yes, and without much drama. Check the listing status and the conservation-area boundary before you buy, because those two flags are the whole difference between a clean project and a slow one.