I've switched off everything that might try to contact the net. In Wayfinder there's an option for updating traffic news. That's off now. And the bluetooth trick works a treat.

So, I'm sorted. What can I say except - thanks!

By the way, interesting using my BT GPS receiver. It locks on to the sats in maybe 30 seconds compared to several minutes with the built in unit.

BUT - my car has an athermic windscreen which is known to interfere with GPS signals. The BT unit is badly affected by this and constantly loses the sats. I have to put it under the rear window. The inbuilt unit in the front, once it finally locks on doesn't lose the signal even on London streets.