From the Global Settings (Home -> Members Area -> Selling -> Seller Tools -> Global Settings) menu select to:
If checked, allows sellers to apply tax on listings.
Select the tax that will be applied to listings.
Note: The tax is 20% VAT applied to residents of the UK.
The seller has the possibility to Apply Tax on a per listing basis from the Create Listing menu:
Log in and the software will automatically apply taxes on products depending on the country of residence (billing address)
The Checkout page will display, in the Review Order section, on the right side of the page, the final price including tax: