Hi,
Si. It's a long time since I worked at the Social over there, but it used to be that the best you could hope for would be to apply for a Crisis Loan from the Social Fund. If they approve it, you'd have to pay it back when your student loan arrives.
Other options are churches, as
Howie mentioned, or getting in touch with a student counsellor at Uni. They should have something in place to help people out who are in your situation. Your bank may grant you an [extension] overdraft for the short term.
As a last resort, you could always sing on the street corner.
Tuna and rice may be healthy food, but not if that's all you're eating.
Good luck in getting something sorted.