I used the North London Line to get from Highbury and Islington the last
two days there were enough people to fill 8 carriages, but only 3 on the
train.

It must be common, because there was no hesitancy getting on board,
everyone runs and crams into every available inch of space.

Is this cattle truck scenario the norm ??

Drifting off from the original subject. I am always amused when I hear the
whining and complaining at East Croydon about supposedly crowded trains in
the morning peaks. Yes they can be extremely crowded but they are as
nothing compared to those I used to encounter in the peaks from Edmonton
Green. They'd have been regarded as half empty there :-)