Presumeably given its location relative to the fence line, it is railway rather than council owned?Sorry, that photo is a bit misleading. It is outside of the railway station fence line (whereas the flood lighting pole is inside the fence line - see
here). Having said that, in the absence of a pavement along the side of the road, it could still be Network Rail's land.
I personally think it won't work because of the adjacent flood lights, but if for some reason it has been kept in light and is owned by the council, it would have almost certainly been converted to sodium by now, as I'm sure Essex don't use 250w mercury anywhere in the county these days!
But if it is Network Rail's, then there's plenty of local railway stations which still use mercury, e.g.
Clacton,
Colchester, so there is a chance!