James,
The manager at the Oxford Branch will deal with OAT students regularly so he'll have his own limits in place. If you try a branch elsewhere I found that the person you deal with may not know as much about the course or the type of loan as the manager at Oxford. This could work in your favour as they may not have as strict limits as to the amount. You have nothing to lose by trying it. At most it will take an hours meeting at the branch.
Another thing to consider, which is likely to be a much easier way of getting a sizeable loan is to take the loan out in your dads name. By doing this he can take advantage of the equity in the house with an equity release loan. This would obviously require the full backing of your parents but it sounds like you already have that. Ask for a Financial Planning Review from the branch and mention that this is what you are looking into
As long as you have the full backing of your parents there will be a way to get more money and probably at a cheaper interest rate. The equity release option is available at other banks as well so if you go for this make sure you shop around for the best rate.
When discussing this with the Oxford branch please do not mention where the info came from. Just say you read about it
