How can I fix my Satellite Navigation System of my Peugeot 406?

The built-in satellite navigation system of my Peugeot 406 (2002) keep saying "Area not digitised". Sometimes however it seems to work, it even speaks to me, the only problem is: I live in Southampton but it thinks it is in Wales!!! I have cleaned the cd-rom player with a cd cleaner but it did not solve the problem...
Does anyone know what to do???
Thanks in advance.
Nick