This is an unusual situation as you offers to pay £15000 in full and final settlement, he wanted £30000 and you agreed to this subject to a further qualification of your receiving a discharge of your liability. So what you have is an offer to settle, a qualified acceptance and a further qualified acceptance, in other words a series of events from your first offer non of which make up a binding agreement. However, he has encased one of your chequers which was tendered on a particular basis, namely that the encashment is deemed to be in full and final settlement. I think that they will argue against you but I do think that you have a stateable case that he has accepted the cheque in part settlement of your offer of £15000 and so is deemed to have accepted that sum in settlement of his claim. I have to say, however, that the point is arguable either way and I've looked to see if there's any authority in case law which would assist. I have found nothing which is why I've argued it for you simply on the basis that there was no concluded contract therefore your earlier unilateral condition applies. I hope that helps. Please leave a positive rating so that I am credited for my time.