Old Railway Hut.

After a good breakfast at my hotel, I drove home from Saffron Walden this morning. The countryside around there is beautiful but I didn't have time to stop this morning. Once home after lunch we went for a walk along the Thames path, unfortunately the sun had gone in by then. I have often wondered about the purpose of this long forgotten building. It is now almost completely covered in Ivy. It is close to the railway but down a steep embankment. Any ideas anyone on its original use?