Career development loan = "Standard" rates of interest!
Forget AST which is a college I believe, and perhaps look at a University offered course (Kingston/Glamorgan etc), where you will be eligible to receive Student Loan from the Govt owned Student Loan company....that way it's funded at a much better rate of interest (~1.5% iirc), and you won't have to put together a "business case" for it like a career development loan.
Another advantage of the Uni/SLC route is that if you are out of work....you don't pay it back (it is taken out of PAYE wages like Tax/NI)....unlike a career development loan, which may result in defaults etc if you can't pay while you are out of work