The Great Northern Railway (GNR) was a British railway company established by the Great Northern Railway Act of 1846. On 1 January 1923 the company lost its identity as a constituent of the newly formed London and North Eastern Railway.
The main line ran from London King's Cross via Hitchin, Peterborough, and Grantham, to York, with a loop line from Peterborough to Bawtry (south of Doncaster) via Boston and Lincoln, and branch lines to Sheffield and Wakefield. The main line became part of the East Coast Main Line.
The Wikipedia page is [1]