If you are applying through a high street bank, your ability to get loan depends on your current account performance (inflow/outflows), You'll have a better chance of being accepted by your own bank where you hold your current account, than applying with a supermarket etc, as they only lend to super prime customers. If you are paying back a student loan, the banks credit system will have calculated this as an outflow and this could possibly affect the decision. The best way is apply on-line as most lenders won't assess your ability to afford the debt in addition to credit scoring.
I'm assuming that you are employment and over 18 you should be OK.. Don't worry about the loan purpose - it's not even used in credit scoring, just say your buying a car or something. Alternatively, you could pay by credit card ( most plastic surgeons accept these). It can be easier sometimes to get a credit card than a loan, although you'll pay more interest overall.