Try reinstalling them using your usual package manager ( synaptic, gnome-package-kit, software… ) or
sudo apt install --reinstall xkb-data xserver-xorg x11-xkb-utilsfollowed by :
sudo dpkg-reconfigure xkb-data
Hey thanks @Coeur-Noir, for this ^^ solution. It seemed to fix the # / £ key on my Macintosh UK keyboard model ‘A1242’ when under the layout English (UK, Macintosh).
THANK YOU!!!