excellent! - I will give that a go and report back - thanks again!

ok - so here is what I found
the file gmapbmap.img was present - I backed up a copy just in case
I replaced it with the renamed version from Garmin as suggested and then did the usual take it outside wait for satellites and tried navigating a route to Swansea
the same "location not found" message came up.
I repeated the whole process of replacing the file and trying it a second time just in case - but the result was the same.

As an observation - if I use the "near" button and try to navigate to say a POI near a city and enter Swansea - Swansea in Wales UK comes up - together with a few other Swanseas in Australia and such like - so does this mean the base map is present and working?