Late in the night of 19 September, the Semi-Fast Mail train was due to call at Grantham. The signalman at Grantham south had his down signals off, but the signalman at Grantham North had all of his down signals at danger and the junction points set from down main to down branch to protect a goods train crossing from the up Nottingham line to the up main line - across the down main line on which the Mail was approaching. It was a clear night with patchy rain, as the Mail roared towards the station passing the south box. When the headlights came into view at the end of the platform, the locomotive appeared to be going much too fast to stop. To the alarm of the postal sorters and the station staff who realised it was the Mail train, it sped towards Grantham North box where the points, which had a speed limit, were set against it. A loud explosion was heard and fire lit up the entire North yard. The locomotive rode the curve, but its long tender derailed on the reverse curve following it and swept away the parapet of an underbridge for, before falling off the edge of it. This derailed the locomotive, which was slung broadside across both tracks. The carriages ran down the embankment after the bridge, and only the last three remained undamaged.
Possible causes
Many explanations were put forward, such as the driver going mad, being drunk, taken ill or having a fight with the fireman. The evidence of signalman Day at Grantham South box was that he had seen both men "standing looking out of their respective glasses in front of them, but they did not actually seem to be doing anything." The platform staff were sure that the brakes on the train were not applied and that it was travelling at over. One possibility is that the driver had a seizure or "micro-sleep" and the inexperienced fireman did not realise until too late. Another, proposed in 2006 in the Railway Magazine, is a brake failure due to incorrect procedures when the engine was changed at the previous stop, Peterborough. The fireman was a premium apprentice from Doncaster works, not a footplateman, and his road experience was limited. If his driver was incapacitated he might not have realised that the junction points were not set for the main line, as both arms of the junction signals were on and gave no indication of which way the points were lying. He might also have failed to reconnect the brake pipe or open the train brake cock. Automatic vacuum brakes were fitted on all passenger trains, so if any air entered the brake pipes due to a failed connection, the brakes would be automatically applied. The mystery remains, not least because a number of Great Northern footplate men testified that the approach to Grantham was unmistakable.
Other derailments
The accident was the second in a series of three derailments due to excessive speed at night in a 16-month period. The others were at Salisbury and Shrewsbury. All three resulted in deaths, including the footplate crews; the cause in each case was recorded as 'driver error' but there has been much speculation since.
