The Welwyn Tunnel on the Great Northern Railway, twenty miles north of London was more than half a mile long. Just after midnight, a unloaded freight train headed north broke down in its middle. Soon after, a loaded goods train entered the tunnel and smashed into the first train. Almost immediately, a third train loaded with meat for London hit that wreckage and a fire broke out. So, three trains were wrecked in one tunnel and the resulting fire burned all day. Scores of workers then cleared the wreckage, remarkably, in time for Monday's rail traffic. Two railroad men were killed in the accident. (By John Osborne)
"Chronicle," The Annual Register: A Review of Public Events at Home and Abroard for the Year 1866 (London: F. & J. Rivington, 1867), 65-68.