The crash occurred at about 13:15 on Sunday, 20 November 1955, at Milton, between Steventon and Didcot on the line from Swindon on the Western Region of British Railways.
The train involved was the 08:30 Paddington station-bound excursion train from Treherbert, South Wales, consisting of ten coaches hauled by Britannia Pacific no.
Because the track involved had been formerly operated by the Great Western Railway, the signals were on the right hand side, but the train was hauled by one of the new British Railways Standard Class 7 locomotives, which had its driving position on the left hand side.
There was a berth track circuit[1] approaching the crossover, but it was much longer than the train, which made it hard for the signalman to estimate the speed of the train.
Handrails on the smoke deflectors also obscured the drivers' view, and these were later removed and replaced with hand holds on all the "Britannia" class locomotives that ran on the Western Region.