Amy,
My first reaction would be to lie about the purpose of the loan .... most UK banks are only too happy to lend unsecured cash to creditworthy clients, and aren't too fussy on checking that you really did buy that car, build that house extension, go for that holiday .... (they factor the risk of unsecured into higher interest rates).
But there again most banks are only too happy to lend for things like plastic surgery, boob jobs, etc, think mine even sent round advertising of the kind "do you want that dream holiday, a new car, the breasts you always wanted ...." as tounge in cheek loan promotion !
Its a fact that even in the UK cosmetic surgery is one of the fastest growing reasons for getting a loan.
So if your bank know about you (guess you've had to change name and gender on your account), see that you're professional and still in good stable employment within your new gender role, and a long standing customer, in all probability they won't freak out over why you need the cash.
I've always found my dealings with financial institutions where I've had to reveal my gender change details to be most pleasant, not least because the counter staff are usually youngish women, who tend to be really supportive and friendly when you drop the "bombshell", full of questions and compliments .... after all you "liven up" their boring and routine day, and give them something to tell their families back home !
The last time I went into a bank having to change details on some old equity investments (only two weeks ago) I ended up chatting with their "personal banking advisor" Debbie for over an hour without finances being mentioned once ! Debbie had asked in all innocence why I needed to change my name (expecting marriage, more likely divorce) and you could see her jaw drop when I said "its a bit embarrassing, but ...."

!!!
Laura
P.S. as you know there's not a big difference between loan sharks an the creit card companies .... I have $40k + available on my two cards, but if I spent that much the monthly interest would eat up nearly a third of my salary !