Yes, and the answer comes with a conservation officer attached. Eighty-five buildings in the area are listed. The old village sits inside a conservation area. Two scheduled monuments sit within its bounds. Extending here is entirely possible, it is just never a decision you get to make on your own.
The listing count is the part buyers underestimate. There are 85 listed buildings in the area, of which 83 are grade two and 2 are grade two star, with none at grade one. Listing attaches to the whole building rather than the pretty side facing the harbour, and it covers the inside as well as the outside. Anything affecting character needs listed building consent, which is a separate application from planning permission and is not a formality: window replacements, internal walls, roof coverings and rainwater goods all fall within it. Doing the work without consent is a criminal offence rather than a paperwork oversight, which is worth knowing before a builder tells you it will be fine.
There is one conservation area, covering Boscastle itself. Designation narrows what you can do without applying, brings demolition and most tree work into the consent regime, and tends to make materials a live issue rather than a detail: slate where slate was, render where render was, and a firm view on plastic. Whether any additional direction applies that removes further permitted development rights is an address-level question for Cornwall Council, not something to assume either way.
Two scheduled monuments sit in the area, and they carry the strictest protection in the system. This matters only if your land includes or adjoins one, in which case consent runs through the national process rather than the council, and the answer to most groundworks is no.
None of which stops people building. The planning register records 122 applications across the area between April 2024 and June 2026, with 47 of those in the most recent twelve months. That is a working stream of alterations in a village of this size, which tells you the system here is navigable rather than closed. What the volume does not tell you is how any individual application fared, and anyone quoting you an approval rate for Boscastle is inventing it.
In practice the village splits into two planning experiences. If your house is unlisted and outside the conservation area, ordinary permitted development rules give you a decent amount of room, and a rear extension is a normal project. If it is listed, or inside the conservation area, or both, assume consent for almost everything visible and budget for matching materials and a longer timetable. Pre-application advice from the council is cheap compared with a refusal.
Freedom to alter your house here is middling: real, but fenced. Boscastle looks the way it does because someone has been saying no for a very long time, and the day you want a bigger kitchen is the day you find out you are on the receiving end of it.