Thanks to Mafia Wars Loot Lady who has generously shared the script in which you can add to your friends edit page on Facebook and it will sort out this horrid little problem very easily!
What it actually does is group together all the deactivated Facebook accounts (the blue ones you see without a profile picture) (Which Facebook added back into our friends list without asking..thanks very much) and remove them, freeing up lots of room for you to add the friends you wish to add. Boom!
If anyone has come across any other scripts on how to remove specific friends etc from Facebook, then please forward! The lesson here? Only add the people you want/need/have to and keep an eye on all the Facebook leavers. Fools.