1. If you've not signed anything in connection with the loan, you will have no liability in respect of any default.
2. A default could affect your own credit rating unless you file a notice of disassociation with the credit reference agencies. You can do this online with Experian:
http://www.experian.co.uk/contactforms/consume r_onlinedisassociation.html
Experian normally pass on such information to other agencies but, to be certain, you might also want to contact Equifax and CallCredit.
Chris