Instructions:My order was delayed and in the e-mail they said "As an apology for any inconvenience that this may have caused you, I'd like to offer you a 15% OFF Promo Code, which you may use as many times you like against all items across the entire website. Your code to use at Checkout is "sorry15". "
Does not seem to have an expiry date, but tested it and took 15% off.
Bonus is you can use it on their January sale items too!
Also you can give Quidco at try too for 10% cashback: