In all the uproar about Bank (I've done a lot of the roaring up), one
question has been niggling away at the back of my mind all along.

That is that the escalators currently being worked on, which are
supposedly at the end of their life, can't have been in use for more
than 17 years (since the DLR extension to Bank opened).

So that means that in an 222 month period, they are out of action for
replacement for 18 months, or just over 8% of the existence of the
route.

So if the course of action while a bank of escalators is being worked
on is not to allow interchange at a station during that period ...

That would mean that an interchange station with 12½ banks of
escalators would be permanently "no interchange" and an interchange
station with 6 banks of escalators would be "no interchange" for
nearly 6 months of every year. An interchange with 4 banks of
escalators would be "no interchange" for 3 or 4 months of every year.

My calculations may be a bit wobbly, but these are roughly the
implications of the policy followed at Bank.