Jointly with my brother and sister, I own a third share in a flat which is not either of our main residential property. This flat was purchased purely for investment. For my third share, only my name is on the deeds. When we sell this flat, can both my legally married spouse and I both claim the CGT allowance? Does my wife's name need to be added to the deeds prior to the sale of property for her to claim her CGT allowance or is it something that, when the money is paid, at that time, can I elect for my third share, 50% should be paid to both me and my wife, thus having not to put her name on the deeds?

In order for your wife to receive some of the sale proceeds, and consequently use her capital gains tax annual exemption, you do not need to add her name to the deeds, but you do need to transfer some of the beneficial ownership of the property to her. If you look at www.hmrc.gov.uk/manuals/tsemmanual/TSEM9520.htm you can see how to do this. You must specify the percentage of the property you are transferring to her. In almost all tax matters it is the beneficial ownership that counts, not the legal ownership.