I very much appreciate all this help - thanks.
I'm going to double check everything in my Wayfinder settings as suggested and then try the selective BT switching. And ther dialog switch off if necessary. It would be good to have the faster lock-on time if my external GPs receiver.
I'll report back when I'e been using the app again for a bit.

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.

Heh, so that icd command of mine worked?