Ten people are injured while police say the incident is not being treated as terror-related.
Two passengers on the Doncaster-London train during Saturday's stabbing attack describe chaos as people scrambled for safety.
Nine people have life-threatening injuries, police say, with counter-terror police joining the investigation.
Defence Secretary John Healey says King Charles has "indicated that's what he wishes".
A company paying Sarah Ferguson was given a private tour of Buckingham Palace while the late Queen was in residence, BBC can reveal.