You probably don't have to worry too much on that count. If you get one, you'll know by email, and they'll give you a reasonable amount of time to respond. Generally my understanding of this situation is that until you expressly give it up, it's yours once they've awarded it (of course, you lose it if you let your admission offer lapse). If you are so lucky as to get the Clarendon, then you need to attach the notice to your college Financial Guarantee form and send that to your college. Also be sure to confirm the offer from your department. Any other requirements to secure the funding will be clarified in the Clarendon letter (again, if you're lucky enough to get one, which I have not as yet).
Any positive responses yet?