I guess this would be my first ever urbex adventure.
I had no idea the tunnels existed. Just happened to stumble across one from an old railway bridge. So I went and took some photos. Upon later research I found there was three tunnels all quite close to each other. These images are taken over a few visits and some long walks!
The Old Dalby Test Track is used for testing new designs of trains. It is between Melton Mowbray, Leicestershire and Edwalton on the course of the Midland Railway's route between Kettering and Nottingham. It closed to passengers in 1968 and is 13.5 miles in length.
After the closure as a through route, it was converted into a test track for the Advanced Passenger Train APT-E project, re-opening in September 1970. The track saw extensive use in the heyday of the Research Division and was used for pantograph development and OHLE testing.
It seems the line is now in use again, should of done more research before going to visit again. Various testing is ongoing for the London underground and sound testing for new Hitachi trains.