I know Arch Linux doesn't hold your hand like other distros do, but I think it could make setting the keyboard layout easier.

Firstly, set the locale in rc.conf:

    ...
    KEYMAP="uk"
    LOCALE="en_GB.UTF-8"
    ...

and then reboot.  Reboot?  Surely there's a better way, but I don't know what it is.

Edit /etc/locale.gen to uncomment the ones you want to use — en_GB.UTF-8 and en_GB in my case.

Then you can run

    # locale > /etc/locale.conf

For 'normal' sorting of ls listings etc., edit /etc/locale.conf and set

    LC_COLLATE="C"

That should sort things out on the console.

For XFCE, it's tricky because the Applications Menu / Settings / Keyboard seems to be ignored.  So refer to https://wiki.archlinux.org/index.php/Xorg#Setting_Keyboard_Layout_With_Hot-Plugging and add this to /etc/X11/xorg.conf:

    Section "InputClass"
        Identifier             "Keyboard Defaults"
        MatchIsKeyboard        "yes"
        Option                 "XkbLayout" "gb"
    EndSection

and restart X.