Noticed this when buying a couple of garden storage boxes earlier, that £10 was deducted automatically at checkout no code required.
Have tried it on a few things, including sale, and it's worked, so looks to be site wide?
Anyway hope it helps someone else!
Don't forget Quidco (exclusive 7% rate)/TCB too.
Credit to the gooner for the added info!
Along with £10 automtically being taken off £30 without needing a code I have also found WELCOME4 which is a £5 off £25 spend code. However, instead of taking £5 off its actually taking 10% off each item so the more you spend the more you save!
My £51.76 order of already discounted items came to £36.75