have you got the handbook,there might be a key number in it,if not go down to your local vauxhall dealer with the V5 and some ID and they will cut a key for you.
perhaps he thinks that someone may find the keys and know whos car it is and drive off in it, whereas if he changes the locks they wouldnt be able to, just a thought!
There are independent auto locksmiths who can change the mechanical locks and reprogramme the transponder unit. Most will be cheaper than the dealer.
For UK and Eire http://www.autolocksmith.co.uk/
This happened to me, I have a 1997 ford mondeo.
The ford dealer can't help even with the VIN no. neither can full membership to AA. Both redircted me to a locksmith.