Hi,
If the UK property was your main residence for the whole period of ownership, then there is no capital gains liability.
If not, then you can claim private residence relief for each month the property was your main residence, plus a further 9 months over the total number of months the property was owned.
You can find a calculator at:
Tax when you sell your home.
As you will be not resident in the UK at the time of the disposal, you will be required to declare the disposal, even if not gain arises.
Thank you