If only a Railview service like Streetview existed. Unfortunately I can't see Network Rail giving anyone permission to film the entire GB network for it be made available to the publc.
There is, kind of, but for engineering and operations purposes. When a full video survey is carried out with the TRU, it's possible to have a basic "streetview" for any stretch of that line. It's a lot more basic than a 360 degree panoramic shot, rather a series of cameras pointing at different angles and synchronised, time and location stamped. For each time/location stamp you could call up a frame from the video from any of the cameras to get a detailed view of the location. The cameras point forward, back, 90 degree left, forwards at 45 degree left and at the right and left rails, and the four foot.