> Though conceivably the break was very small and a train impacting the slightly lifted rail just caused a good chunk of it to explode.

The crown (top) of the rail seems to be missing after the gap. The crown-less section then continues ~3 meters before it disappears behind the investigator on the left. IDK what that might indicate.

ref pic: https://ichef.bbci.co.uk/news/1024/cpsprodpb/ecb4/live/53924...

The rail is laying on its side in that picture, so what is visible is the foot not the web.

edit: other angles of the same location here: https://youtu.be/DIQ4SrGSua0?t=1174