Why bother getting the key cut if it doesn.t open the door, could be the locks have been swapped or mixed at some point, if it has, probably easier to get a good second hand lock set and keys from somewhere.
cos presumably it started the car
Well yea, obviously I appreciate the key worked in the ignition, the point I was on about is the key may or not fit the door, wouldn't be the first time Ive come across an Omega where the Ing Key doesn't work on the doors, because its been swapped out in its previous life, you normally find out when the battery is flat or the fob's packed up.
If it was me, I'd be thinking a couple of steps ahead before buying blank keys or issuing the VX Dealer with my open wallet. The OP has still got the key blade, so that can be investigated further to see whether it fits the door lock or not.
Hopefully its a stick'y lock, if its not, dont think I'd be getting another key cut just for the Ing. probably get the whole set sorted out with a second hand setup.