Amazingly, no one seems to have actually checked that this picture was really "circulating on social media". I've been investigating for the past hour or so and can't locate a single public post or reference anywhere other than reposts of the BBC article.

Typically, postings that gain traction have many many reposts and though some may be deleted, there's a long tail of reverberation left behind. I can't find that at all here.

I wonder if the hoaxer just emailed it to Network Rail directly?