Thanks Dave & John.
I thought I might be able to do an update myself, but as I cannot even see the places where I need to unscrew the facia etc, I don't think it's worth it.
I put one of those magnets on the vents on the dashboard above the SatNav etc & stick an old Samsung S7 edge phone there with Googlemaps & it also a brilliant SatNav program called OsmAnd+. I even take it abroad & it's fantastic.
It's just such a shame that I can't have an up to date display on the Car SatNav. Never mind - c'est la vie I suppose!