Mostly yes, as long as you are not in the old core. Listed buildings are few. There is one conservation area. The neighbours file plans constantly. Cliffe is a village where the extension question is usually about the ground and the budget, not the heritage.
Cliffe has 15 listed buildings: 1 at Grade I, none at Grade II*, and 14 at Grade II. Listing covers the whole building, inside and out, so any change that affects its character, from an extension to a replacement staircase, needs listed building consent on top of any planning permission. Owning one of the 15 means owning a relationship with the conservation officer. For everyone else in a village of hundreds of homes, the count is small enough that listing will not be the obstacle.
There is 1 conservation area, covering the historic Cliffe core. Inside it, changes that would be routine elsewhere, such as altering the front of a house, some demolition and work to trees, can need consent, and the design will be read against the character of the street rather than your mood board. Outside it, those extra layers do not apply.
The planning register is the best evidence that people here do alter their homes. Between April 2024 and June 2026, 689 planning applications were logged for the area, 292 of them in the last twelve months. That is not a village frozen in amber. It is a village where somebody on most streets has a set of drawings and a builder who says he can start in the spring.
The ground is where the real homework sits. The British Geological Survey rates shrink-swell clay risk at class 3 across all of Cliffe's postcodes, and compressible ground reaches class 3 in about 81% of them. Those are published hazard classes, not a verdict on any one plot. Clay that swells in winter and shrinks in summer moves foundations, and ground that compresses settles under new weight. For an extension, that means deeper foundations than a builder might quote for firmer ground, and a structural engineer's view before the price is agreed. The cheapest quote on marsh-edge clay is usually the one that forgot about the clay.
In practice, a house outside the conservation area and not listed will often have permitted development rights, which allow some extensions without a full planning application, within national limits. Inside the conservation area or on a listed building, assume consent is needed and check with Medway Council before paying an architect. Either way, confirm that the specific property has not had its rights removed by an earlier permission, because a previous owner's planning history travels with the deeds.
Freedom to extend is one of Cliffe's quiet advantages: heritage limits touch only a small historic corner, and the bigger constraint is what sits under the lawn.