CGT on commercial property converted to residential and incorporated into residence above

We own the freehold of a former Sui generis property which was purchased derelict 6 years ago. The ground floor was converted into A3 commercial use and the first floor was converted into a flat and has been used as our primary residence approximately 15 months after purchase and only home ever since. We own no other property. We are currently applying to extend our residential dwelling into the commercial space below (A3 commercial use) due to our growing family and more rooms required. Should we sell, what would the capital gains tax implications be?

Hi
We cannot comment on future events as legisltation and/or circumstances may change.
Based on current legislation, a gain would occur on the A3 section of the property as this was not part of your main residence for the whole period of ownership.