Katya Tasheva

Hello I need to sell art print I own , it’s not original artwork. it was a Birthday gift from a friend some years ago. There is no way to know the price of this item at the time of gift. My guess it was not more than 2500-3000£. Now it is estimated by auction platform 7000-10000. But no exact price. How do I work out if it’s taxable or it’s similar to watch is not? And if taxable how do I calculate the tax?