While on a 50 mile trip today the sat nav started OK but then went haywire after about 6 miles. It is seeing the data base but appears  not to be recieving the GPS signal. Perhaps the GPS receiver is faulty or the aerial. Is the plastic aerial on the roof the GPS aerial I believe sometimes they are embedded.in a door window like a heated screen. Has anyone experienced anything similar. I have the Skoda extended guarantee but not sure if this includes Satnav.

Not experienced it myself

However, unless you are in the first year of ownership from new or subscribe to Skoda Connect you won't be getting live traffic.  Would personally recommend Android Auto (or the other one) as it will be a real time as you can get with Google Maps or Waze 

Google maps is far superior to the Skoda Navigation. You'll of course need a reasonable smart phone and to connect it with a cable, but once you start using it, you'll not want to use Skoda Nav.

I have wireless AA as does my wife on her Karoq