Found this on the website:
Unconditional Firm Offers
If you are an undergraduate applicant and went unconditional firm with us by the beginning of July, then your tenancy agreement will be sent out to you this week. In order to confirm that you want the room we have allocated to you, please sign both copies of the tenancy when you get them and return one to us as soon as you can. If you are away travelling, just ask a parent to sign on your behalf and return the tenancy to us. We will ask you to countersign once you arrive at Sussex in September.
Hopefully I will get mine tomorrow or I'll just call up.