I still couldn't get this straight in my head, so I worked some basic numbers:
IGNORING INTEREST (because the difference is not much really):
PCP:
£21000 cost
£5000 gfv
£16000 loan
36 month term
£444.44 monthly
Loan from the bank:
£21000 loan
48 month term
£437.5 monthly
If you stop at 36 months into the 48 month term, you still owe the bank £5244.... which is roughly your GFV.
So you only have the advantages of interest rates to gain really.
BUT one more thing I will say... a PCP credit agreement is easier to get because you do not own the car. Its a secured loan.
A loan from a bank is just a cash loan, they probably will ask for detailed income statements etc etc and may not lend money to a student, unless your parents guarantee it...