There was a met station at this location up to 2006 but finding the Stevenson screen is a poser. It might be on earlier Google images, Bing is no help and it is screened from the road.
Some kind of golf course later on.
The site was a sewage works WW2, a major London reservour is close as is I think the river Enfield, a canal, power lines, mass of things, none important other than clues might be anywhere.
I’m up to things, the pause has been about detail work unearthing, surprises coming of a long arm nature.