The Highway Code is not law, but it does include many points of law (denoted by the word must in bold type).
However failing to observe the code, while not in itself an offence, may be taken as evidence of 'driving without due care', a catch-all charge covering the many types of blithering stupidity perpetrated by the vast majority of road users.
In law, of course, ignorance is no defence, so even if you haven't read the Highway Code for 20 years you can still be prosecuted for new offences.
A more serious point underlies this: many motorists are guilty of a fundamental lack of attention. We have ALL done one or more of the following while driving (myself included), talk, make phone calls, smoke, tune the radio, change the CD, re program the Sat Nav, unwrap sweets, check the delivery sheet address, - all things which take our attention away from the road.
At 56mph a car covers 25m every second - in the time it takes to change a CD you might take your eyes off the road and travel over 100m. At night, on dipped headlights, you can see about 75m. That means you can't afford to take your eyes off the road at all, because the distance you can see to be clear is about the same as your stopping distance. And you should know all this because it's all in the Highway Code.
At the end of the day however, if people don't even know how dangerous their behaviour is, they won't change it.