Yes, but you will be asking permission more often than you would like. There are well over a hundred listed buildings. Two conservation areas cover the old centre and Sheet. The whole town sits inside a National Park. The neighbours apply for planning permission in their hundreds anyway. Extending a house here takes paperwork and time, so do not plan on it being quick.
There are 139 listed buildings in and around Petersfield: 2 at Grade I, 6 at Grade II star and 131 at Grade II. Grade II is the everyday tier, and it still covers the inside of the building as well as the front. Changing a listed home needs listed building consent on top of any planning permission, and that includes internal walls, windows, fireplaces and the staircase you were hoping to open up. Carrying out works without consent is a criminal offence, not an administrative mistake, and the next buyer's solicitor will ask about it.
The Petersfield and Sheet conservation areas add a second layer. In a conservation area, work that would elsewhere go ahead without an application, such as some extensions, cladding, dormers or felling a tree, can need consent. The council looks at whether a change preserves the character of the street, so the plastic bay window that went through unnoticed in the next town becomes a formal submission here.
There are also 15 scheduled monuments nearby, most of them Bronze Age barrows on Petersfield Heath. Scheduling is the strictest protection there is, but it only affects land on or next to a monument. Unless your garden backs onto the Heath, it is unlikely to come up.
None of this stops people. Between April 2024 and June 2026 the area logged 1,509 planning applications, 658 of them in the last twelve months. That is a steady flow of kitchens, loft rooms, garden studios and tree works being put in front of the planners. People in Petersfield do alter their homes. They do it through the proper process, and they take longer about it.
The ground needs its own check. The British Geological Survey puts the area in shrink-swell class 3, and all of the area reaches that class. That means clay that swells when wet and shrinks when dry, which moves foundations over time. For an extension it usually means deeper foundations, advice from a structural engineer and a building control officer who takes an interest in nearby trees. It adds to the cost, not to the danger, provided it is priced in from the start.
In practice, a modest rear extension on a post-war house outside the conservation areas and away from the listed buildings is an ordinary job, subject to National Park scrutiny. Anything visible from the street in the old centre, or anything touching a listed building, should be treated as needing consent until the planning department confirms otherwise in writing. A pre-application conversation costs less than a refusal and less than an enforcement notice.
Freedom to extend is one of Petersfield's weak points: listing, two conservation areas and the National Park together make many changes a matter for consent rather than choice. It can still be done, but it takes time and a patient architect.