Historically the Midland Railway, serving points north of London. But unlike other main lines north of London, did not extend as far north as Scotland.
Extensive reconfiguration completed in 2007 enables station to accommodate Eurostar trains using the Channel Tunnel, in addition to trains using Midland Main Line. Eurostar trains use newly constructed high speed Channel Tunnel Rail Link (CTRL) between St. Pancras and the Tunnel. Midland trains continue to use Platforms 1-4 (and underground ThamesLink platforms A-B). Eurostar trains use Platforms 5-10 in a secure zone. And domestic trains to southeast England using Channel Tunnel Rail Link use Platforms 11-13. The ThamesLink route extends further south and south of Blackfriars Station.
MAIN LINE: St. Pancras-Bedford and beyond
4 tracks St. Pancras-Bedford
From west to east, pairs of tracks identified as Fast, Slow.
Additional Lines:
Moorgate
Moorgate Line is a 2 track alternate line serving London used by ThamesLink trains via tunnel, connecting with main line at Kentish Town.
All lines AC electrification.
CHANNEL TUNNEL RAIL LINK: St. Pancras-Channel Tunnel
2 tracks St. Pancras-Channel Tunnel
All lines AC electrification.
Indedepently operated high speed line connecting St. Pancras Station with Channel Tunnel. Original line opened in 2003, including connecting segment from Southfleet Jn to Fawkham Jn, where connection would be made with Chatham Main Line into London. Final segment north of Southfleet Jn opened in 2007, mainly using tunnels north of Thames River. One short interruption of the tunnels is at Stratford International station, in vicinity of 2012 Olympic Games.
Number Of Platforms/Tracks: 13 (plus 2 underground through)
Platforms numbered west to east
Underground platforms A and B are used by through ThamesLink trains, and connect with the Slow Line north of the station.
St. Pancras Station
Wikipedia link containing further station information and history.