The Rail Accident Investigation Branch has started an investigation into a derailment near Bletchley in Buckinghamshire in June 2025.

The derailment occurred at about 12:27 on Thursday, 26th June 2025, at Denbigh Hall South Junction on the West Coast Main Line when the front bogie of an out-of-service London Northwestern Railway passenger train became derailed.

The train was travelling north at approximately 15 mph (24 km/h) on the up slow line shortly after leaving Bletchley station when it became derailed on a switch diamond crossing. Four members of staff were on the train, but there were no reported injuries.

Some lines through the junction remained out of use until 16:05 on Sunday, 29th June 2025, while the train was recovered and the infrastructure was repaired.

Earlier that day, while the train was operating a southbound passenger service, it had suffered a technical problem and was unable to depart southwards from platform 4 at Bletchley.

However, it could be driven northwards, allowing it to be moved clear from the platform. There was only one signalled route from the north end of platform 4, which had previously been occupied by a failed on-track machine.

Staff at Rugby Rail Operating Centre then decided to allow the train to travel in the wrong direction on the up (southbound) slow line, which required the signaller to instruct the driver to pass the north end platform signal at danger and travel to Denbigh Hall South Junction without the normal protection of signalling interlocking.

At Denbigh Hall South, the intention was that the train would cross onto the down slow line where it would once more be under normal signal control, and would continue northwards to Kings Heath depot near Northampton.

The investigation will look at the sequence of events leading to the derailment, including:

• What were the actions of those involved, and were there any factors that may have influenced them?
• How unscheduled movements are determined and validated.
• The management arrangements for the staff involved in the accident, including how those undertaking such movements are trained and assessed.
• Whether any relevant underlying factors could have contributed to the derailment.

In February, the Rail Accident Investigation Branch released a report into a derailment last year in Norfolk.