The Student Room Group
The HSBC Gap Year account currently has an interest rate of 18.6% EAR for overdrafts. Not sure as to how much you can have, but I'd imagine it's like a normal bank account, where you can have it within reasonable limits, if it's pre-arranged.

I'm on HSBC Gap Year, and I'm making sure I don't touch a penny of overdraft!
I got the brochure through a while back but from what I can recall, the overdraft is about £250 I think.