Yes, if your house is ordinary. If it is old and pretty, you will be asking permission more often than you'd like. Nearly 150 buildings are listed. Four conservation areas cover the historic core and its edges. The neighbours file for planning permission constantly, so it can be done. The catch is the paperwork, and the paperwork is set by the age of your house, not the size of your plans.
Alton has 145 listed buildings: 1 at Grade I, 4 at Grade II* and 140 at Grade II. Listing covers the whole building, inside and out, not just the front that got it onto the list, and changes that affect its character need listed building consent on top of any planning permission. The buyer who assumes the listing only protects the frontage tends to learn otherwise over a kitchen wall. With 140 of them at Grade II, most listed homes here are ordinary working buildings of their period rather than showpieces, which is exactly why owners forget they are listed until the builder asks.
The town has four conservation areas: Alton itself, Anstey, Holybourne and The Butts. A home inside one isn't frozen, but changes that would go ahead without permission elsewhere may need it here, and anything visible from the street gets a harder look. Being in a conservation area is less of a constraint than being listed. The trouble is that it covers the streets people want to buy on, which is where the plans tend to start.
Alterations do happen. East Hampshire's planning register holds 1,338 applications for the area between March 2024 and June 2026, including 587 in the most recent twelve months to June 2026. That is a town busy with extensions, alterations and change, and a planning team that is kept busy by it. The number tells you how often people ask, not how often the answer is yes, so don't read an extension on the next street as a promise for yours.
In practice, the house matters more than the town. A post-war semi outside the conservation areas is likely to have the usual permitted development rights for modest rear extensions and loft work, subject to the national limits and whatever conditions the original planning permission attached. A listed cottage, or a house inside one of the four conservation areas, needs checking before you commit to anything. Before an offer, find out whether the house is listed, whether it sits in a conservation area and whether the permitted development rights have been removed, and ask the sellers for the planning history of anything they have already changed. A solicitor will find some of this. A conversation with East Hampshire's planning team, before you exchange, will find the rest.
For anyone buying a project, Alton gives you less room than the listings suggest: the character that sold you the house is the thing the planning system is there to keep. Buy the older homes for what they are now, and look to the post-war streets if the plan is to build.