When installing my system, I selected to encrypt access to my system. This prompted me to enter a password. I entered a password with a # symbol in it, however due to using an english keyboard, this would not have been correctly recorded as a #, but as a ' instead - leading it to refuse my password when booting.
I tested this both connected to and not connected to the internet.
It seems that at the point of entering the password during the installer, the keyboard layout was set to en_US. Therefore, when booting and having the locale as en_GB - it didn't correctly work.
I tried this with the @ symbol, which when entered was accepted on boot by hitting shift+2 (american combination)
I also tried this by entering a password with a £ sign (shift 3 on UK keyboard - which would be a # on a US keyboard)
When entering password on boot, entering the password with the # key rather than the £ key worked.
In summary - when entering password for encrypting system, keyboard is set as a US keyboard layout, which differs from that when booting to enter the password if it is changed in a later step.
Proposed solution: Move the keyboard selection / Locale Setup before any input boxes. (espescially those where you can't see the contents of them!)
<http://goo.gl/YwIcT>: "The “Keyboard layout” screen should appear immediately before whichever is the first keyboard-requiring step."
<https://goo.gl/lDfhcI>: "Whenever “Encrypt the new Ubuntu installation for security” is checked, the caption 'You’ll choose a security key in just a moment.' should be sensitive. 'Choose a security key' is a keyboard-requiring step, so that typing the security key works as expected."
It may save time to fix this at the same time as bug 871752.