I and others I know were involved in passenger assistance that morning further down the line, purely as a result of being around on the way to work (as usual), and as it turned out I later learnt of work colleagues who were on both trains, but thankfully survived.
There are times in one's life when it is said that one always remembers where one was/what one was doing - and that morning is one such occasion, when everything is as clear to me today as it was then, but after getting to work in Waterloo around lunchtime, everything afterwards is a complete blank.
A very dark day for all concerned.