 At the same time, electrification started with the installation of a 25 kV overhead line to cater for suburban services as part of the Great Northern Suburban Electrification project.The works were completed on 3 April 1977, and electric services began running from King's Cross to Hertford, and 

The construction of the Victoria line and its interchange at King's Cross was seen by British Rail as an opportunity to modernise the station.A single-storey extension containing the main passenger concourse and ticket office, designed in house, was built at the front of the station in 1972.