[3] Twenty-four two-car units were built by British Rail Engineering Limited's York Carriage Works in 1990 and 1991.

[1] Following the privatisation of British Rail, the fleet was sold to Porterbrook and operated by Southern up until late 2013, when they were transferred to South West Trains and heavily refurbished.

[8] Entry into service for the Class 456 was originally planned for 18 March 1991, with trains to be driver-only operated (without the presence of a guard).

To resolve this Selhurst depot designed a replacement fixing for the driver's seat so that it could slide sideways, allowing a good view of the CCTV units.

[9] The modified drivers' seats were installed at Fratton Depot with the work completed by the end of July 1991,[7] and services with the new units commenced in September 1991.

456024, was repainted in white and yellow Connex livery, when it was named Sir Cosmo Bonsor after a chairman of the South Eastern Railway.

In 2000, Connex lost the South Central franchise to the Go-Ahead Group, who rebranded the company as Southern in 2004.

[13] Southern also received 26 new 5 car Class 377/6 units and these entered service at the end of 2013, in place of 92 cascaded carriages promised for extra capacity.

Despite this the Class 456 EMU trains lost two seats from each pair, due to a space being cleared for wheelchairs and pushchairs.