Yes, in rural locations the UK postcode 'area' can be quite big and the lat/long position could be in the middle of a field. Most satnavs will guide you to the nearest road to that position, which may be the wrong road. In towns they usually get you to the correct street IME.

Some cheap phones don't have gps at all and google will use position based on cell towers, wifi access points, and (it's rumoured) nearby phones. Wifi-only iPads used not to have gps chips - maybe still don't.