The MS&LR was formed by the amalgamation of the Sheffield, Ashton-under-Lyne and Manchester Railway with two proposed lines – the Sheffield and Lincolnshire Junction Railway and the Great Grimsby and Sheffield Junction Railway, with its headquarters at Manchester London Road. The Sheffield, Ashton-under-Lyne and Manchester Railway had opened between Manchester and Sheffield in 1845, but as early as 1844 the promoters of the Sheffield and Lincolnshire Junction had approached the SA&MR with a view to the latter leasing it. The Great Grimsby and Sheffield Junction had been promoted by the Grimsby Docks Company, actually the oldest company of the three. Until reaching south with its "Derbyshire Lines", the MS&LR was essentially an east-to-west Trans-Pennine line.