The Natural Philosopher gurgled happily, sounding much like they
were saying:

I'm not a truck driver, so I don't know if that's the case or not. If
it was, I'm sure the haulage firms would be restricting their driver's
speeds - yet they aren't.

yes they are, I've seen several artics with stickers on the back saying
"this vehicle is restricted to X mph" where X is lower than the 56 mph
limit (and I don't mean the 40 mph limit on single carriageways).

Is that for efficiency reasons or for PR to try to cut back on the
"dualling artics"? I suspect the latter - because it would be FAR more
widespread, especially amongst smaller/pikier outfits - whilst the ones
who seem to do that seem to be the more "polished".

50mph on single carriageways....

Nope... 40mph. 50mph is only for 7.5ton.