It is just as illegal to drive distracted by a satnav as it is to drive distracted by an iphone in the UK. If you're holding it in your hand or looking away from the road to use it, then it is illegal.
Even if you aren't holding it in your hand of looking away from the road, but are significantly distracted, you can be prosecuted under the "Driving without due care attention" law as you state.
> It is just as illegal to drive distracted by a satnav as it is to drive distracted by an iphone in the UK.
Correct. However it is illegal to use a phone without being distracted dangerously, whilst using a satnav without being distracted dangerously is perfectly safe.
The Driving without due care and attention is a perfect catch all for dealing with bad driving behaviour. You can be done for eating crisps as easily as using a sat nav. The specific "using a mobile phone whilst behind the wheel of a car is 6 points on your license + a fine" is completely disproportionate in terms of what behaviours it implicitly approves (such as using sat nav safely whilst not moving) and the burden of proof (requiring the user to be "unsafe").
The reality is that policemen (of whom there are simply not enough) have discretion and a bit of common sense most of the time and use the tools at their disposal to punish people for driving badly whilst using their phone. This is good. I fundamentally disagree with singling out unsafe mobile phone use in law, however.
Even if you aren't holding it in your hand of looking away from the road, but are significantly distracted, you can be prosecuted under the "Driving without due care attention" law as you state.