Found this on internet:
Users manual - check out page 104, select units from the settings menu and set it to Great Britain. Think it defaults to Europe-SI for some reason, when the battery has been disconnected etc.
http://www.vauxhallownersnetwork.co.uk/index.php?threads/change-odometer-units-from-km-to-miles.231953/
ChicksFan, December 2014