Our Saturday walk, after passing the aggressive cows, took us along the Thames for a mile or two of the Thames Path. At one point we saw a very cool bunker, and poked around a bit.
It was well concealed from the river behind some trees and was at a location with a good view both upstream and down.
I found online that these are called ‘pillbox’ bunkers and that they are quite a few remaining from WWII, scattered around England particularly along the coasts and rivers. While searching I also found this article on one that has been cleverly incorporated into a home’s landscape design.