I am guessing that the problem was the Jubilee Line being suspended NOG
to Stratford due to a conked out train. Given the Central Line is above
the Jubilee Line at Stratford it is possible that you couldn't see how
congested other parts of the station were. I'm speculating that letting
lots of people off Central Line trains who then head to a non operating
Jubilee Line is not the best option. I also suspect that DLR was
horribly oversubscribed but it also seems to have had problems according
to an apology poster I saw on my way home tonight.

I see - thanks for that - that must have been the reason. I did indeed
notice the DLR platforms looked busier than normal. What is strange is
that the Jubilee Line has been suspended loads of times and I've never
known them not stop Central Line trains....