On the Chiltern Main Line, the snow caused tree branches in the cutting at Seer Green to be weighed down and some of them were brushed by passing trains.

On 11 December, the driver of an empty train from Marylebone to Princes Risborough came across a fallen branch lying across the track.

Meanwhile, at Gerrards Cross, behind the stationary train, the driver of the 07:31 from Marylebone to Banbury was being cautioned by the signalman about the overhanging branches.

Glancing again at his diagram, he saw that the lights towards Beaconsfield were not in fact lit, and realised that the empty train was still in the section near Seer Green.

Although British Rail's rules stated that the guard of the empty train should have applied detonator protection, this would have been unreasonable given that the obstruction would have been cleared in a few minutes.