Various infantry bunkers laying about are also a reminder, but what really gets me are the bonkers last-ditch defensive weapons you can still find in places, like preset positions for flame fougasse batteries:
I think we are seeing similar tactics and mobilization in Ukraine. They had to invent and be practical on the battlefield without the overwhelming numbers of the Russian empire.
https://en.wikipedia.org/wiki/Flame_fougasse
They speak to the particular combination of desperation, urgency, and ingenuity found in the UK at that time.