Hi Jilly. As a rule, an extension is likely to be less contentious than an annexe at the planning permission stage, especially if the latter is self-contained.

Your mention of a separate address and council tax liability are both things that are suggestive of a new, separate dwelling – rather than an annexe – and should be avoided. If the planning officer is happy with the layout and regards it as merely an extension, then apply for it as such. As you are one family then how you divide up and use the internal space of the dwelling, once built, is of no interest to the planning system – assuming you don’t entirely subdivide the property. Maintaining internal doors between the main house and annex is important in this regard.

If your application suggests you’re trying to create what is effectively a new self-contained dwelling, then it’s likely to prove far more contentious, especially in AONB countryside.

Mike Dade, Build It expert and planning consultant at Speer Dade