Hi Andy,
As you will be the principle on the Loan agreement, most of the credit rating will go on you - although it obviously does strengethen things if your parents are guarantors.
Unfortunately the loans companies are right on this one - if you want to benefit from a decent rate (sub 15% APR), the agreement will have to be in the name of somebody with godd or half decent credit. In your case, your parents.
Sorry
Tim