If you cannot find your "Car Pass" card (it's about the size of a credit card, so check through any paperwork, service book, etc) you will have to go to a Vauxhall dealer to get a new one.
You will need to take the cars V5 doc, receipt/proof of ownership, and proof of your identity (photo driving license, recent utility bills etc.).
Price varies, some (a few!) will do it free, usually £25/£30.
There will also be a charge to program the key to the car, cheaper getting this done at an independent.
Timpson key cutters seem to be quite good, but never used them myself.
heo
December 2010