So I recently had an explore of the mysterious 'Northern City Line' in London. As I'm sure many of you know, travelling on this line is like being taken back in time. Its stations seemingly have had no renovations since the 1980s, and the line has an overall 'creepy' atmosphere. It seems a world away from the sleek, clean, clinical, modern London which can be seen on the surface. It also seems to have different laws from the rest of the UK.... I took a few photos at some of the stations there, when suddenly approached by a worried station staff member (which surprised me, as they are rarely seen). "You're not allowed to take photos here!" . I then politely explained how wrong he was. He's only response was to say I will be reported to the authorities, which is rather concerning. I'm well aware of Company TOCs and Railway Byelaws, but is there a special rule for the 'Northern City Line'? Or maybe having to work deep underground in a damp time-warp has made Great Northern's staff a little grumpy. I regularly take photographs across the UK rail network (and in Europe), and have never had any problems taking photographs. Except on the Northern City Line on three separate occasions (the two others a few years ago) Usually if i'm taking a large amount of photos on the rail network, I tell a station supervisor. But i've never seen one on the Northern City Line to ask - they just appear out of the darkness only when I take a photo.