Tried that, and it said:
eCoupon not added.
Save £10 when you spend £40 or more at Tesco direct
You've not met the minimum spend. Please add more items from the eCoupon promotion to get your discount. Delivery costs are not included.
Cheeky Tesco! They have lowered the pre-order price from £40 to £39.99 to prevent people from using the code. Solution: Add something else cheap with the game. Basically your total needs to be £40 or more for the discount to apply.