London Girl,
I have no idea about the maximum amount that the bank will allow you to borrow. I also know how much you want to fly, I'm there! However, from someone who has seen it go wrong over and over again:
Think VERY carefully, long and hard about this. There are other ways and means of getting the funds, it will take longer yes.
I know that being able to fly NOW is a very tempting offer but once you have been in the (not so stable) industry for a few years, other things start taking a priority, a house, family, life etc.
Think about it.
jau