Pretty skilled bit of flying in manual mode.

How to fly a drone through Crossrail's tunnels - BBC News (http://m.bbc.co.uk/news/business-31820033)

Presumably outwith the jurisdiction of the CAA? :-)

But not the HSE I am quite sure.

*Civil Aviation Authority
**Health & Safety Executive

Very cool location, not sure why they didn't shoot it with a better camera, GH4 or 5D3? They make it sound like that was difficult to do. That was about as easy as it gets.