Key snapped

Did the key break off in the cylinder or do you mean the cylinder turns free without moving the ignition switch? In the first one you can make a broken key extractor easily. The fastest way is to use a fish hook that you straighten. To use it you slip it in on the cut area of the key then turn it so the barb catches the key to remove it. A small paper clip or other stiff thin wire will work as well, you just need a barb or in the case of wire, bend it into a tight bend and cut one side at a sharp angle.

If it's the second one you will need to remove the cylinder from the column and then replace the switch activation pin. Being a 2003 you may not find those parts on the shelf but a salvage yard might have them.

If you are trying to release the steering lock by force, you will likely damage the column itself. If it is stuck you would need to remove the covers to get to the switch assembly. Then remove it to get to the steering lock.

They normally will have a couple screws underneath and then clips that hold them together. Once those are off you should see the bolts that hold the ignition to the column. There doesn't seem to be access to the service information on that van online. I'm still trying to find accurate info on it, if Citroen has it.