If you get £1000 on top of the basic salary you are being paid, then surely you pay back the loan that you arranged for training i.e. you are paying back money incurred for the training.
As a lot of others have said on this thread, you could think about it as having some training costs paid for and a reduced salary, or having the full salary (inc the £1000 a month) and pay back the loan yourself.
CTC use the former for marketing purposes...from their website.
"The CTC Wings Cadet Programme is a sponsored programme, which means you won't be paying for your training....however you will be required to raise a security bond."