They are doing extensive fencing all along that part of the line I travel frequently - even where you'd think the risk of trespass is quite low, like Potters Bar & Hadley Wood tunnels. It's ugly palisade fencing, the concession to toning down by application of green coating being well offset by shiny vicious 'chariot blade' capping. That'll stop enthusiast photographers poking their lenses over the top!
I have to say it heightens my feeling of a country no longer at ease within itself whenever I travel, but then there have been well-publicised accounts of essential railway cabling being stolen from tracksides, and that is perhaps most likely in just the kind of quietly rural stretches I have noted.
Being a railway model maker with a fondness for the local scene (as was), I must get out and take detailed measurements of the old order before it's too late. Back in 1974, I made quite detailed measurements of Brookmans Park's footbridge.
