"Shall not" would be compulsory, "should not" is advice.
Splitting hairs, but traffic law is not criminal law. Then driving isn't a right either. It's a privilege that's conditional on passing a test & following the rules of the road.
Regarding the updated code....
My daily is a lentil muncher's eco special edition that displays smugness stats. I usually pedal my regular "commute". If I chicken out 'because it's raining & take the car I'm lucky to log an average 15mph, even though the speedo gets up to 30 between lights & junctions. Conclusion: cyclists don't often slow you down, you just get to the bits that do slow you down quicker if you pull a dodgy passing manoeuvre on them.
Comparing mpg, I get about 40 keeping up with traffic, I have managed to hit 70 on the same run across town when the roads are empty by avoiding braking, anticipating traffic lights & driving as slow as possible in 5th (25-30mph).
