In practice the bar for "due care and attention" is low (ie. you have had to be really, really careless or really, really inattentive to be convicted). The courts in the UK hold drivers only to a pretty low standard in general. That's why they had to pass a separate law to ban handheld use of mobile phones.

An example of how oblivious drivers on phones are is this:

I parked (where I could not be seen by the van) to warn oncoming drivers of mobile speed van 50 metres ahead over brow of hill.

While nearly all made eye contact with me and speeders instantly slammed the brakes, two drivers on phones (both women with kids), despite me flashing my headlamps AND putting my hand out of my car and waving at them, they still did not look at me or put down the phone.

This was after the penalty was doubled to 6 points.

(And yes I know its not legal for me to warn drivers of speed traps like this)

This can be a fixed penalty (no court involved unless driver does not accept penalty). So I think it really depends on what the driver was actually doing (especially impact on driving), how the driver responds to being stopped by police, and whether police is having a bad day.