The SVR locomotive was travelling along Victoria Bridge between Arley and Highley at about 1.30pm yesterday when the driver spotted what appeared to be a man running along the track and another lying alongside it in an extremely dangerous location.
Train driver Dave Evans said: “I could not believe what I was seeing, and it was lucky I managed to stop the engine. These two men were putting themselves in huge danger.
"The one lying beside the track was wearing a climbing harness and had attached ropes to this and to the rails and bridge structure. He was clearly preparing to climb over the edge and lower himself down below the arch or may have already done so.
"I told him how dangerous this was, and he said it didn’t matter because the railway was closed.”
Dave was able to capture some video footage of the incident and this has now been given to the police, who confirmed they attended but found nothing of concern at the time and were continuing to investigate.
The Class 33 heritage diesel locomotive was hauling engineering wagons as part of the railway’s maintenance programme and there were no other people on board. The railway is currently not running public services but continues frequent and unscheduled operational movements of rolling stock.
The railway’s general manager Helen Smith said: “Not only were these men risking their own lives in what they were doing, but they could also have put a member of our staff at risk as well.
"We have had a number of trespass incidents in recent weeks, but this is the most serious.
"Just because we’re not running public services does not mean the line is safe. We operate many non-scheduled engineering and maintenance vehicles on a daily basis, and people are risking their lives by trespassing on railway property. Please keep off the track and railway property.”
A West Mercia Police spokeswoman said: "At about 1.30pm on Thursday we were called to reports of antisocial behaviour on the Severn Valley Railway bridge. We attended but found nothing concerning at the scene. We are continuing to investigate and ask anyone who may have seen anything or has concerns to contact us through the Tell Us About section of our website."
It comes after the railway issued a number of warnings to the public last year when people were regularly seen trespassing alongside the tracks, despite locomotives still operating on a care and maintenance basis.
Anyone with any information should contact police on 101 or through westmercia.police.uk
The force advise anyone who sees someone trespassing on railway property to call 999.