From 1 April 2016, Stamp Duty Land Tax rates change to introduce an additional 3% duty on any property bought, where the buyer already owns a property in their own name or jointly with others.
If you do own another property which you are intending to sell after your purchase is completed, then you can then claim back the additional 3% duty provided you complete your sale within 36 months of your purchase.
More information can be found on the Government's website.