You will need to check your parents' policy and/or phone their insurer to check, the policies themselves vary from company to company.
On my motor policy as well it says I am insured to drive any privately insured motor car. (providing certain other criteria are met also)
Does a privately insured van class as a motor car ?
Who is to know who you are when you are driving it, you go out and drive. Just take it easy and don't look suspicious, If you get stopped do the following:
a) pretend to be your father
b) offer the police officer a bribe
c) start a chase with the police, with the cut backs they will not be able to follow you for too long