Many thanks, Chris!
The mail train thing was a very happy coincidence! I play an awful lot of Simsig Kings Cross (1955 steam timetable is the best!) and have always wanted to try creating a scenario based upon it. I just happened to start planning a scenario around this particular train as it left Kings Cross and went from there. The same is true for my other scenario, although the decision to use the particular service was based upon certain interactions along the way...
I actually popped in to post this up, which I thought was quite amusing.