From the Wikipedia page 
The London, Tilbury and Southend Railway is an English railway line linking Fenchurch Street Station in the City of London with northeast London and the entire length of the northern Thames Gateway area of southern Essex. It is currently known as the Essex Thameside Route by Network Rail and forms part of strategic route 6. It is classified as a London and South East commuter line. Train services on the line are currently operated by c2c, a train operating company that is part of the National Express Group.