On the NCL-KGX service on which I travelled on Monday, there were repeated announcements (from before the start) that there would be no trains south of Peterborough, and that anyone wanting to go to London or other destinations south of Peterborough should not travel, and their ticket would be valid the following day. Perhaps someone has taken the view that anyone who ignored those warnings and decided to risk it (as I did!) should not expect a free ride back if they effectively changed their mind?
What I was more concerned about was that I needed to spend two days in London (i.e. Monday and Tuesday, returning on Tuesday night). If I had aborted the outward journey, as advised by EC, OK I may have got there on Tuesday on my original ticket, but would I have been able to change the return journey to Wednesday free of charge? I somehow doubt it!