This goes for all Merlin parks in the UK (except Legoland cos it looks like hell on earth).
Years ago, when purchasing a ticket, on the reverse side there would be an offer to return to the park the next day at a heavily discounted price, last time I went it was like a fiver to return the next day.
Does this offer still exist? I was planning of making a trip to Alton Towers at some point by buying a ticket on the day and then using Bounceback but I am unaware if the Bounceback offer even exists anymore.