rights, no you are not liable till you sign. However as a landlord I take a pretty dim view of students who turn up wanting keys without the guarantor paperwork in place. Its only happened once, where one boy's mother signed up but the other mother refused to. The agent gave them the keys telling me it was fine. I was appalled. Yes if there had been a problem we could have pursued the guarantor for the whole amount. But that was hardly fair on her. I ended up saying that if both guarantors had not signed as promised, I would use the six month contract break clause.
Both boys were lovely, as was the flat, which I don't normally let to students. Bottom line is that if parents don't trust their children enough to act as guarantors, I don't see why I as a landlord should.
That said I completely get the issues with students who cannot find guarantors or struggle with getting the money together for a deposit. It can be a real problem. My flat is slightly away from the University so student tenants need cars. The current overseas students and their friends are bemusing neighbours by driving expensive sports cars, though are polite and seem to study hard.
When people are talking about "deposits" up thread, are you sure you are not talking about "holding deposits" to the agency to secure the property, rather than the protected deposit, normally one month's rent, that landlords will almost certainly require before keys are handed over. At the moment it is also legal for agents to charge tenants for drawing up agreements, taking references etc, though this will change next year.
The girl DD is most likely to share with has been invited to join another group from her course, but is not sure. DD is sitting back waiting to see what happens. She is optimistic that a place will turn up somewhere, either via sports or course friends. And if not she can look at studio/private hall options. Though her flat has calmed down a lot, she wants to avoid the problems faced at the start of the term.