For those of you frustrated that you can’t perform a trivial task such as producing #’s, £’s and even @’s without RSI-enducing key combos on your Mac, then you may be interested in setting up a British Keyboard Layout so that you can get full use out of your trusty Model-M.
First off, big thanks to Phil Gyford, this is mainly just a mirror of his excellent guide with a couple of changes. The main annoyance I was having was that the “International” keyboard switcher (the little flag icon up in the top right) would not let me remove the “British” keyboard layout which was installed by default (the one you are probably lumbered with now, right 
. The instructions below get around that problem, but as they involve a bit of screwing around I recommend you back up all you data first, yadda yadda.
- Open Finder, navigate to /System/Library/
- Drag the “Keyboard Layouts” folder to your desktop (it will copy, not move)
- Delete the contents (yes all the bundle files) of the “Keyboard Layouts” folder from/System/Library/Keyboard Layouts (please make sure you have a backup – you will need it in a moment!)
- Now download the Mac OS X British Keyboard Definition file.
- Unzip it to /System/Library/Keyboard Layouts – it will now be the only file in there.
- Open International which is in System Preferences
- Select the Input Menu Tab, this will show a list of possible keyboard layouts.
- Select (check) British – Windows 2
- Deselect (un-check) British (this would have been grey’d out if you had not removed the .bundle files from /System/Library).
- Close International.
- Copy all the .bundle files which you backed up on your desktop into /System/Library/Keyboard Layouts.
- Logout and log back in.
- Enjoy your new found ability to type #’s in a single keystroke!
To make things a little simpler, here is a screenshot of International with the British – Windows 2 keyboard definition selected (and that pesky British one removed!). Your keyboard profile shouldn’t randomly switch back to the default Mac one anymore.
This for this, it semi worked… when I put the bundle file back into/System/Library/ the original British was still checked and greyed out, and it kept changing back to the original British all the time, and never remembered my choice of “British – Windows 2″ in the menu. So I decided to rename the AppleKeyboardLayouts.bundle file to AppleKeyboardLayouts.bundle.old so it would not be used, so the only option I have now is the British – Windows 2 so it cannot revert back.
The only problem which is major is when I log out the keyboard is not recognised, so I cannot enter my password to login. I have to restart the Mac which does not ask for a password, else I think I would be in trouble.
I cannot enter my password in any password box in order to rename the bundle file back to fix this issue! Had to remove my password in order to put the file back.
So therefore the proper solution above does not work for me as it keeps reverting back to the wrong British for the keyboard I am using.