Friendofmaddo, the difficulty with asking people - even, in fact especially, current students - is that the procedures develop and information becomes out of date year on year (even if it was accurate in the first place). It is therefore always appropriate to contact the Admissions Office of the college handling your application for definite advice. Subject to this qualification, I'll tell you what I know.
Once your results are received, the college from which you have a conditional offer will confirm the offer if you have met it. If you fail to meet the conditions (whether by missing a STEP grade or otherwise), they may confirm the offer anyway. Alternatively, in this situation, your application may be made unsuccessful - though hopefully this won't happen of course! A third possibility on a missed offer, however, is that you may be placed in the Summer Pool for consideration by other colleges who, after confirming offers for their candidates who have met offer conditions, still have places to fill.
If this happens, then - assuming my information isn't out of date - your UCAS page would still show your offer as "Conditional" when you checked it on results day. I think if you rang the college admissions office, then they would tell you that you had been placed in the summer pool. The Pool takes place very soon after results come out, and on an extremely tight time schedule with no interviews held (so it's really not akin to the long and drawn-out Winter Pool process). Another college, if it has places to fill, may then make you an unconditional offer through the Summer Pool if it chooses to do so.