Yes, if the promotion is offering a free gift with purchase, there is no problem with using your Gift Card in conjunction with this. Simply place your order as normal and apply your Gift Card code once you reach checkout. You can find further instructions here.
If the promotion requires you to enter a discount code, it's a little more complicated but don't panic - we have a solution!
Due to the way that our system works, it's only possible to enter one Gift Card or promotion code per order. This means that you only have the option of using one or the other so if you would like to use both simultaneously we ask that you please enter the code for your Gift Card. Then just email your order number to our Customer Experience Team along with the discount code that you would like to use and we will be able to refund this retrospectively.
You can also get hold of our Customer Experience Team via Live Chat on our website or by giving us a call. You can find the correct phone number for your region here.