After a little digging around I came across this article which provided the simple solution. Have a look at your /sys/module/hid_apple/parameters/fnmode file:
Chances are that its value is 1. We need to set this to 2.
We can do this by editing the /etc/rc.local file
sudo vim /etc/rc.local
Add the following lines before the exit 0:
#Added to enable the apple function keys by default.
echo 2 > /sys/module/hid_apple/parameters/fnmode
save, exit and reboot your system.
Before you give the function keys a go, have another look at the /sys/module/hid_apple/parameters/fnmode file. It should have a value of 2.
After this I discovered that function keys F13-F19 did not work! Sigh. I created ~/.Xmodmap file with the following entries
keycode 191 = Insert
keycode 192 = Print Sys_Req
keycode 193 = Scroll_Lock
keycode 194 = Pause Break
keycode 195 = First_Virtual_Screen
keycode 196 = Next_Virtual_Screen
keycode 197 = Last_Virtual_Screen
add Shift = Shift_L Shift_R
add Lock = Caps_Lock
add Control = Control_L Control_R
add Mod1 = 0 Alt_L 0x007D
add Mod2 = Num_Lock
add Mod4 = Super_L Super_R
add Mod5 = Mode_switch ISO_Level3_Shift ISO_Level3_Shift ISO_Level3_Shift
keycode 0x7D = equal
This file will be referenced the next time you log in and all should be sweet in the world! :)
And that it should be it.... until the next Ubuntu release!
Also have a look here for alternative solutions.