I am a non-UK resident with two let properties in the UK. I intend to sell one. How long would I have to reside in the property that I wish to sell for it to be considered my main residence, therefore not attracting capital gains tax (CGT)? 

Arthur Weller replies:  

Even if you now start residing in the UK property, this will only take away the CGT from now on; it will not take away the accumulated CGT to date. For example, assuming you bought the UK property for £200,000 in 2014, if you now start living in it as your main residence and sell it in 2029 for £500,000, you will have made a gain of £300,000. Of this, £100,000 will be exempt (i.e., 5/15th of the gain), but £200,000 (i.e., 10/15th of the gain) will be subject to CGT.