From Brightwells "How To Buy" page:-
A buyer’s premium at the following rates will be added to the hammer price:
For Vehicles - 10%+VAT (minimum of £150) (e.g. on a hammer price of £10,000 you pay £1,000 premium + £200 VAT to give a total of £11,200, assuming a VAT rate of 20%)
For Automobilia and all other items 17.5%+VAT
*Items in this sale sold subject to VAT in addition to the hammer price are marked with an asterisk.