[1] The Southern Region of British Railways 23:12 electric passenger train travelling from London Waterloo to Windsor & Eton Riverside and Chertsey collided with the rear of a LMS class 8 2-8-0 hauled freight train from Herne Hill to Brent at about 35 mph.

The coaches were classified as 2-NOL and were converted in the 1930s from old London & South Western Railway steam carriages.

A manual release key could be used to circumvent this interlocking if, for example, a broken mechanical link or track circuit gave a false indication of a train on the line.

A contributory factor was the failure of the circuit breakers supplying the traction current to the section to trip when the collision occurred – the subsequent arcing and fire caused most of the fatalities.

One of the passengers killed was Bernard Crouch, an England table tennis international and world championship medallist.