Ziggy thanks for the update -
I had the exact same thing with my MPG display when I bought my car.
I asked the dealer to look at the problem and they suggested that a very expensive sensor would need replacing but after they reset the computer in house the problem was solved and I was not charged. One of the reasons I travel 19.9 miles to them as I receive an honest quality service..
WESTS OF BEDFORD
87 HIGH STREET CLAPHAM BEDFORD MK41 6AQ Tel 01234 354257 Fax 01234 212815
I am not entirely sure this would work for you but it did in my case.