Thanks to SkyBlu75 for posting the codes.
Smyths have quite a few lego offers on at the moment ie 20% off Selected DC, Marvel & Ninjago Sets + Free Delivery on Lego when you spend £15. They have also just released some money off codes ie £5 off £20 (SEP5), £10 off £50 (SEP10) & £20 off £100 (SEP20). These combined offers & the code SEP5 makes the fab LEGO Superheroes 76031 Age of Ultron: The Hulk Buster Smash set just £16.59 Del.
Site is well worth a browse with the combined discounts & codes.
Original price gone up to £23.99 so offer is now £18.99