This has been discussed here before: standing people pack tighter than walking people, therefore all standing ends up with more throughput, at the expense of lower individual latency (for the would-be walkers).

But you only need that optimization when escalators are at full utilization. In many cities, escalator discipline is low enough that the walk/stand lane pattern deteriorates when the escalator approaches maximum capacity. The minority who don't get it and rudely block the walkers accidentally apply the throughput optimization. London seems to lack a reliable distribution of rude blockers who would accidentally optimize for throughput when necessary, so they need to search for an explicit solution.

> standing people pack tighter than walking people, therefore all standing ends up with more throughput, at the expense of lower individual latency (for the would-be walkers)

If the would-be walkers derive much greater than average utility from a quick journey, isn't it likely that the all-standing regimen achieves higher average throughput at the expense of lower average utility?

When there are enough passengers to saturate full all-standing throughout, reducing throughput to allow individual latency improvement will soon cause waiting times before the bottleneck. Once a sufficiently long queue has formed, newly arriving walkers will not have a quicker total journey than they would have had under throughput optimization with shorter (or no) queues.

London has sufficient loud walkers prepared to yell "Excuse ME!" when blocked.

And not enough of them in my opinion! It is a population where people will endure a lot of things before they lose their courtesy. People eating smelly food, stinking up a whole car. I have even seen some dude getting in a car with a bucket full of fresh fish and no one made any remark. A few angry eyes at most.