Ok, I pulled the unit from the boot (trunk) and the antenna connection was a little wobbly, so I removed it and plugged it back in and secured it with tape.

On start-up, the status now showed RECERR, so I went for a drive. After 3 or 4 minutes, it changed to SEARCH, then to TRACK.
It found 6 of the 8 satellites (cloudy day) and the Sensor Check screen showed as 'Position Known'
I could also see lots of dots on the top right icon in the monitor.
Let's see if it loses itself again now....