I don't understand why you would struggle to deduct VAT, it is added onto your purchase price and all trade prices are excluding VAT, so if you buy at £100 + VAT your purchase price would be £120, you then mark up the product by your desired amount and then add VAT to it to find the selling price, so with a 40% mark up the price would be £140 + VAT = £168.
Buzz is correct with his calculation for deduction for overseas buyers. As a VAT registered company you can sell overseas with no VAT on the sale to save the buyer from reclaiming, I used to handle VAT free sales in the drinks trade, many to the Channel Islands.
The sum to deduct VAT is roughly 16.67% of the total cost.