Okay, just followed the advice in this thread
http://www.navitotal.com/forums/showthread.php?3114-Completely-Stuck-ONE-XL-with-Work-Truck/page2
and in particular this post by djc
http://www.navitotal.com/forums/showthread.php?3114-Completely-Stuck-ONE-XL-with-Work-Truck&p=17406#post17406
and it is now working w00t.
Just one problem though, it is as slow as anything, the device reports (when I can eventually navigate there!) 0.0mb free :O
I was reading something about clearflash tool but does it erase any information that is possibly needed (favourites etc.) as this is not my device!
Thanks