Usually, yes, and South Cerney is easier to extend in than its old centre suggests. Most of the village is newer housing with no listing on it. The old core is a conservation area. Fifty-seven buildings are listed. Which of those rules apply depends on which side of the old village edge the house stands.
Historic England lists 57 buildings in and around South Cerney: one at Grade I, none at Grade II*, and 56 at Grade II. Listing covers the whole building, inside and out. Most changes, from a new window to a removed internal wall, need listed building consent on top of any planning permission, and doing the work without it is a criminal offence. A listed house can still be extended, but the conservation officer gets a say in every detail.
There is one conservation area here, covering the old village of South Cerney. Inside it, the council looks harder at anything visible from the street. Some changes that would need no application elsewhere need planning permission here, and taking down most buildings or felling a sizeable tree needs notice to the council. On Cotswold District Council's online maps, check whether the house is listed and whether it sits inside the conservation area boundary. The two layers can apply to houses on the same lane quite differently.
The area also has two scheduled monuments, one of them South Cerney castle. Scheduling is the strictest protection there is and covers the ground itself. It matters mainly if your garden borders one.
The planning records covering this part of the Cotswolds hold 2,829 applications between April 2024 and June 2026, with 1,311 in the last twelve months alone. People here alter their homes all the time. Whatever you have in mind, the planning department has very likely seen something like it already.
The British Geological Survey puts every postcode in South Cerney in class 3 for shrink-swell, meaning clay ground that swells when wet and shrinks when dry. That isn't a reason to give up an extension. It means a structural engineer should look at the soil, the foundations may need to go deeper than standard, and the trees near the new walls need thinking about. Put the engineer's fee in the budget at the start, alongside the architect's.
In practice, the answer depends on the type of house. Only about 12% of homes here were built before 1930. The post-war and later houses that make up most of the village, outside the conservation area, generally have the normal permitted development rights for rear extensions and loft conversions, subject to the usual limits and to any conditions on the original estate permission. A listed house, or one in the old centre, means applications, drawings and patience. You can live in South Cerney without going near a conservation officer, as long as you buy a house that doesn't need one.
Your freedom to extend in South Cerney is middling overall. It's fairly free for the newer houses, tight for the historic core, and every house sits on clay that needs an engineer's attention whichever group it's in.