Thank you for your reply.
You could both be liable to capital gains tax when you sell the flat at a future date as it won't be your main residence and private residence relief would be restricted to period the flat was your main residence.
If your fiancee is added to the mortgage deed of new family home then there are no CGT implications. On the otherahnd, if she is added to the mortgage deed of the flat then she could be liable to CGT on the gain over and above the valuation now.
[q] Does getting married before or after this property deal take place, have any bearing on capital gains tax which she needs to pay?
[a] if she is added to new home, there should be no CGT as it would be main residence. If added to flat, there could be CGT payable on sale whether married before or after property deal takes plaace.
My aim is to give you a professional service. I hope this is helpful and answers your question.
Please remember to rate my service by selecting the 5 stars at the top of the screen before you leave JA today. If you need more assistance, please use the reply box below and let me know. It has been my pleasure to assist you with your question.