I just fixed a rattle from that area the other day. I always though it was coming from somewhere on the dashboard.
I found out that it was actually a loose screw located below the steering wheel just to the right (T25 drive).
Try banging on the top of the dash with your fist. If you get the rattle then look under the steering coulmn and keep bashing the dash. Now try tightening this screw and see what happens. This screw was very loose on my car and tightening it stopped the rattle. I guess this will be an issue in all Leons as the dash has never been apart before and the rattle got steadily worse.
Good luck