EDIT: credit should go to chanchi who posted the code stacking deal. Apologies I didn't check the B&Q drill deal before posting this.
2 promotional codes can be stacked currently at B&Q online.
It will restrict you to one promo code on mobile and tablets. But if you log on via a PC you can add both codes successfully
After adding the item to your basket and selecting delivery method, go to checkout, scroll to the bottom and clicked click 'Add voucher'
EMAIL4759 (10% off total order)
CLUBD86SF (£10 off orders over £50)