The Redhill incident in the thread above, has reminded me of the incident at Dovey Junction, circa 1964, in the early days of DMUs on the Cambrian, (when steam was also still about). One evening, after dark, an up DMU from the Pwllheli line arrived at Dovey Junction. The usual token exchange took place, the signalman receiving that from Aberdovey and handing the driver one for the section to Machynlleth. But he had not yet set up the route. In a classic "buzz buzz and away" departure the driver started, without checking the signal. The points lay set to a long siding on the up side (sometimes used for stabling stock in summer I think) and the driver accelerated away on this siding, not realising he was not on the main running line! The DMU demolished the stop block and its front vehicle ended up, minus bogies, on the boggy ground. I don't think there were any serious injuries but it must have been quite a shock to those on the train.
The DMU was a Park Royal one which ended up in preservation on the West Somerset, but which, the internet informs me, has since been scrapped.
An item in either British Railways Illustrated or Railway Bylines, I cannot recall which, sometime since 2010, and which I have no longer got, featured pictures of the DMU and of the recovery operation, which I think involved two steam locomotives.