vortex

Hello, I would like to confirm that full VAT can be claimed when purchasing an item using an external source to fulfill the same value at a discounted rate for example: Vendor A provides gift cards that can be used to purchase items from Vendor B but at a discounted rate for example a £100 giftcard for £90. Using this £100 giftcard that I purchased for £90 I purchase an item from Vendor B for £100 and on the VAT invoice it shows the full £100 spent, with according £16.67 VAT for it. I would like to confirm that I can still reclaim £16.67 for this purchase and that I should put down £90 as the cost in my books?