The rise of the commuter in the South East of England meant the network of lines and stations serving London were very well used into the 1980s, the London and South East sector was crated to initially manage these routes in 1982. The intention was for L&SE to be able to cover costs with operating revenue, thanks to these large amounts of passengers making use of the service. A new image was formed from the original London and South East sector in 1986, with Network SouthEast superseding the brand following the launch by new Director Chris Green. 

Network SouthEast launched with their brand new Red, White and Blue livery at Waterloo station during 1986, with the intention to paint stations, rolling stock and various other infrastructure in the colour scheme in three years by the end of 1989. Not only was this a rebranding, it also came with substantial investment and improvements to service standards, with investments made in improvements to stations, infrastructure and rolling stock. Many trains that had begun development during the British Rail era were introduced during Network SouthEast including the Mk3 derived Class 319, 321, and 442, as well as the newly developed Networker family.

The Networker family of trains were announced as a part of the launch of Network SouthEast in 1986, to replace much of the remaining slam door stock on the network. The family included the diesel Class 165 and 166 ‘Networker Turbo’ and electric Class 465 and 466 ‘Networker’. The Networker Turbos would see use on the Thames and Chiltern divisions while the Networker electrics would see use on Kent Link services out of London to Kent. Following the introduction of the original fleets and the eventual cancellation of the ‘Universal Networker’ programme, the Class 365 ‘Networker Express’ units were ordered to fill the need for more units on Kent Link and Great Northern services. The final units rounded out a fleet of 344, and while operations of Networkers were widespread, the project never achieved its aims of completely replacing slam door stock in the South East.

Network SouthEast began the process of privatisation in 1994, with the sector separated into 11 different operators. The goals of Network SouthEast not all the goals had been met by the conclusion of the sector, as much of the slam door rolling stock remained in service thanks to the cancellation of the Networker plan. Many of these units would see use into the mid 2000s, before privatised companies could introduce new trains to fully replace these fleets.