In message , at
13:17:12 on Sun, 25 Nov 2012, Portsmouth Rider
remarked:
See Highway Code Rule 243.

That's a "Do Not", rather than a "MUST NOT".

I just KNEW you were going to come out with that. Now... why do you think it
says "Do Not" and not "MUST NOT"?

(I know the answer to that, I just want to see if YOU do.)

It says "Do Not" rather than "Must Not", because it's a statement about
driving behaviour and not the law.

Some driving behaviour is so bad that it's also against the law, but
much of what the Highway Code recommends needs to take the local
circumstances into account and is therefore not subject to a blanket
legal prohibition.

So, for example, it's not that bad to block a bus stop to drop someone
off, if there's only one bus an hour, and the last one that day ran
several hours previously.
--
Roland Perry