I purchased a house with my partner (not married) in 1993 for £53,000. We separated in 2000, and I bought her out for £16,000 as the value of the house had risen to £90,000. In 2011, I purchased another property and let this one out, so for the purposes of CGT can I add the £16,000 to the £53,000 to make my purchase amount of £69,000? 

Arthur Weller replies:  

It is not clear to me why you paid your ex-partner only £16,000 in 2000 if the value of the house then was £90,000, instead of paying her £45,000. It could be that she owned less than 50% of the house, (i.e., maybe she originally (in 1993) paid for only about 18% of the house). So, to answer your question. If in 1993, both you and your partner paid for 50% of the house (i.e., £26,500 each), and then you acquired the other 50% of the house in 2000, when the market value of that 50% was £45,000, then if you sell the whole house, your base cost for CGT purposes will be £26,500 plus £45,000 = £71,500. This can be seen in HMRC’s Capital Gains Manual at CG14530. But if she only paid for 18% of the house in 1993, and you paid for 82% of the house, i.e., you paid about £43,500, then when you sell the whole house, your base cost will be £43,500 plus £16,000 = £59,500.