student ids will really leave you in the dark sam, most places only accept driving licenses + passports, hell, i've had a friend refused service with a "pass id" id-card type thing that has a sole purpose of stopping you having to take your driving license or passport out.
If you don't have anything and you're really desperate, well, there are a few places where you can get a legal ID in under 2 weeks, but it wont be cheap. But really, take down your passport if you have one. The chance of you losing it is pretty minimal if you're careful.
eg:
http://www.proofgb.com/
£22.