The main topic and outcome of this thread seems to have been missed by most.
Buy a used Micra key from eBay for about a tenner, ensuring it includes ALL internals (including the important black transponder chip), get a new blade cut from a local shoe repair/key cutting specialist, swap the blades over then follow the re-coding procedure linked to above. If you're struggling to remove the blade, maybe take the Micra key along with you when you get the blade cut and ask them to swap it over.
I've got a rather large watch. I recently tried four high street jewelers when I needed a new battery. Each one I visted was slightly more 'classier' than the one before (read 'classier' as 'cost of stock') and not one of them could fit the watch into their 'watch battery changing equipment' and each said it would be needed to be sent away to their specialists, with costs increasing from £20 upto £50! For a new battery!!
Popped to the local shoe repairer and he just laughed. 3 minutes and £9.95 later, I had a ticking time piece again
Moral of this story - don't buy a stupidly big watch