Is it an original Vauxhall locking key?
If so, take it to the dealer and get them to match it up. Most dealers carry a full set of locking nut keys (Ive had to do this with Nissan and BMW), so they bring a case full of key to the car, try each one until they find one that fits, and then sell it to you (Last one I got was from BMW and it cost £7), and then relace it for themselves for stock in the future.
....of course, it wouldnt surprise me if Vauxhall didnt do this - something that makes so much sense, yet they are oblivious

Failing that, take it to a garage and get it removed - wont cost much, and should damage the wheels....