I am intending to build a new house in my garden in London, and then sell off the existing house which is currently my main residence. I will then move into the new house, which will become my new main residence. The build cost will be approximately £100,000. The completed value will be approximately £200,000. Will I be liable for stamp duty? If so, is it on the value of the land before construction, the cost of the build, or the final value?

Arthur Weller replies:
You cannot be liable to stamp duty land tax (SDLT) unless you buy something (see HMRC’s guidance at www.gov.uk/hmrc-internal-manuals/stamp-duty-land-taxmanual/sdltm00260). In your scenario, you are not buying anything. You are just building a house on land that you already own. So SDLT is not relevant to you.