@Peter Griffin
As far as I understand it, the £84k bond paid by you is simply a means of covering BA's back to make sure you complete training to their set levels. If you fail training, BA is not out of pocket. If you complete training and go on to work for BA then they pay the £84k bond back over 7 years because its a 'sponsored scheme'.
However you choose to finance the bond is up to you. If you finance it yourself then BA will pay you back the £84k bond so the training is effectively sponsored by BA and you come out with £0 expenditure for training (roughly). If you get a loan, BA pays back the £84k bond as above, but this time you will have accrued interest on the loan you took out so you will have a sizeable expenditure at the end of the 7 years! The £12k per year is a repayment of the training costs (bond), not a repayment of the loan so it is irrelevant as to how you finance the bond, you will always still get £22k starting salary + flying allowances + £12k per year for 7 years. Obviously if you have £84k lying around down the back of your sofa then its better to use it than to get into £1000's in interest over the repayment period by using a loan... but many people (myself included!) will have to use the loan.
Thats how I see it anyway.
Hope this helps.