From the website
"If you are offered a place, you will be informed by the College and through UCAS. You must reply, observing UCAS requirements and deadlines. If you accept Cambridge ‘firmly’ you must meet the conditions of your offer (if your offer had conditions attached) by 31 August 2009. In a few cases, applicants who have not quite met the conditions of their offer may still be offered a place, either at their original College, or at another College as a result of a small ‘summer pool’. "