The discovery of bomb-making notes on a train sparked a bank holiday security alert.
Armed police were called in to search two trains at Luton station last night after cleaners found documents describing "how to make a bomb", Bedfordshire Police said.
The notes were found at 8.23pm while one of the trains was at Bedford Station, and it left for Luton with around 50 passengers before the staff could raise the alarm.
Police cleared the passengers off at Luton, searching that train and another one which had also arrived from Bedford.
Both trains were delayed for nearly an hour before the all-clear was given, when the trains and their passengers were allowed to continue.
A force spokesman said: "We can only apologise for the inconvenience that was caused...but in light of the information contained in the notes found it was felt necessary to take this course of action.
"A thorough search of the carriages was necessary not only to capture any additional evidence that maybe present but also to ensure passenger safety.
"Once we were satisfied that their safety could be guaranteed, we were happy for passengers to continue on their way."
Inquiries into the notes were continuing, the spokesman added.