Let's say you borrow the £120k, you get the job at the end of training and you can pay back the money no problem! Guess what happens next.... life happens....you meet a bird, you decide to get serious, you end up married, she is expecting and you want to buy a house ..... bla bla bla etc etc ...... believe me, it'll all happen very quick!
As great as flying an airliner is, it's still just a job! You need to have a life outside of flying to keep you sane, its very hard get on with the rest of your life when you have £120k on your credit report!!