2007 Opel Corsa ignition barrel emergency

Cut two thin strips of paper the same width as the key. Slide one into the cylinder on each side of the slot, past the broken part of the key. Mix up a tiny dab of epoxy, apply it to the end of the part of the key in your hand, and stick that in between the pieces of paper. Use a wire or rubber band to hold it in position while the glue sets up. The paper will prevent the glue from sticking to the sides of the slot.