[2] Accordingly, NX and rolling stock lessor Porterbrook placed an order with Alstom for the construction and delivery of eight eight-car units, enough to run services at 15-minute intervals at peak times.

Only after an extensive program of repairs and modifications by Alstom did the fleet's reliability reach a level sufficient to allow full withdrawal of the ex-BR stock in 2005.

[10] Following the June 2009 renewal of their contract to operate the South Central franchise, Southern leased and refurbished the remainder of the Class 442 fleet for use on Gatwick Express services.

[15][16] The units of this "new" fleet would be used—either individually or in pairs of ten cars—to provide extra peak-time capacity on suburban services to and from London Waterloo.

[17][18] The Department for Transport announced in December 2011 that it had accepted the proposal,[7] and an agreement between Porterbrook and South West Trains was signed in January 2012.

[13] New Train Management System (TMS) software was developed to be compatible across the entire Class 458/5 fleet, simplifying maintenance and improving reliability.

[7] An Automatic Selective Door Opening (ASDO) system was installed for use at a small number of stations where it was impractical to lengthen platforms.

SWT expected to receive the first two converted Class 460 units in May 2013—in time for them to enter service the following November—but due to delays in production the initial delivery didn't take place until October.