Complex sentence: The GN&SR was backed by the Great Northern Railway (GNR), the main line railway operating from King's Cross station, which saw the GN&SR as a means of relieving congestion on its route.
Split into simpler sentences: The GN&SR was backed by the Great Northern Railway (GNR), the main line railway operating from King's Cross station. The GNR saw the new company as a means of relieving congestion on its route.