|Try booting a Live CD/USB, mount your install partition and edit
# If you change any of the following variables and HAL and X are
# configured to use this file, then the changes will become visible to
# X only if HAL is restarted. In Debian you need to run
# /etc/init.d/hal restart
# The following variables describe your keyboard and can have the same
# values as the XkbModel, XkbLayout, XkbVariant and XkbOptions options
# in /etc/X11/xorg.conf.
XKBLAYOUT="gb" # <<<<--- there it is, here: gb for british keyboard
# If you don't want to use the XKB layout on the console, you can
# specify an alternative keymap. Make sure it will be accessible
# before /usr is mounted.