Editing Brighton Main Line (section)

===Nationalisation (1948{{endash}}1996)===
[[File:(The former) Balham signal box - geograph.org.uk - 899090.jpg|thumb|right|Balham signal box opened on 12 October 1952 and closed on 7 June 1981.{{sfn|Mitchell|Smith|1987|loc=Fig. 70}}]]
Under the [[Transport Act 1947]], the Brighton Main Line became part of the [[Southern Region of British Railways]]. During the 1950s, work continued to modernise the signalling system, which included the installation of colour lights between Selhurst and East Croydon in March 1954.{{sfn|Mitchell|Smith|1988a|loc=Figs 99, 117}} In the same decade, the number of signal boxes on the line was reduced and new boxes were commissioned at Balham,{{sfn|Mitchell|Smith|1987|loc=Fig. 70}} Norwood Junction,{{sfn|Mitchell|Smith|1988a|loc=Figs 103, 104, 108}} Gloucester Road Junction{{sfn|Mitchell|Smith|1987|loc=Fig. 101}} and Purley.{{sfn|Mitchell|Smith|1988b|loc=Fig. 31}}

The South Terminal at Gatwick Airport was opened on 9 June 1958. The new terminal was directly linked to a new railway station on the Brighton Main Line, which had opened on 27 May that year. The former airport station, located close to the redundant Beehive terminal, had closed on 18 May 1958.{{sfn|Oppitz|1987|pp=73-74}}{{sfn|Mitchell|Smith|1988b|loc= Fig. 111}}

[[File:BREL_Class_455_No_455841_(8061890234).jpg|thumb|right|A [[British Rail Class 455|Class 455]] unit at {{rws|Sydenham|London}} in [[Network SouthEast]] livery]]
On 4 January 1982, the Brighton Main Line and the majority of the Southern Region of British Railways, became part of the new "London & South Eastern" sector of British Rail. Four years later, on 10 June 1986, the sector was rebranded to become [[Network SouthEast]].{{sfn|Brown|Jackson|1990|pp=7-8}}

In the early 1980s, a major resignalling project was undertaken that involved the closure of the majority of the signal boxes on the line and the transfer of control to Victoria and Three Bridges signalling centres.{{sfn|Mitchell|Smith|1987|loc=Fig. 20}} London Bridge panel box, which had opened in 1975, retained control of the line north of Norwood Junction.<ref name=Clarke_2020/>{{sfn|Mitchell|Smith|1988a|loc=Fig. 16}} Remodelling of Windmill Bridge Junction was undertaken, with the creation of an additional flyover to eliminate conflicting movements between trains on the slow lines.<ref name=Clarke_2020/>{{efn|The embankments required for the creation of the new flyovers at Windmill Bridge Junction were constructed using spoil from [[Betteshanger Colliery]] in Kent.<ref name=Clarke_2020/>{{sfn|Mitchell|Smith|1987|loc=Fig. 104}}}} The arrangement of the tracks at East Croydon was changed to route all fast services through platforms 1, 2 and 3 on the west side of the station.{{sfn|Mitchell|Smith|1987|loc= Map XXIII}}

[[File:73208_at_Horley.jpg|thumb|right|A [[British Rail Class 73|Class 73]] locomotive in [[InterCity]] livery operating a Gatwick Express service in push mode]]
Gatwick Express services were launched by Network SouthEast on 14 May 1984 using {{cvt|90|mph|adj=on}} capable [[British Rail Class 73|Class 73]] locomotives in push-pull mode, each hauling a rake of [[British Rail Mark 4|Mark 4f]] coaches and a [[British Rail Class 414|Class 414 (2-HAP)]] driver motor brake unit.{{sfn|Glover|2001|pp=79-80}}{{sfn|Oppitz|1987|p=75}} The journey was timetabled to take 30 minutes and seven trainsets were required to operate the service.{{sfn|Glover|2001|pp=79-80}}<ref name=Foster_2014>{{cite magazine |last= Foster |first= Suzanne |date= 18 November 2014 |orig-date= 11 June 2014 |title= "Catch the train and you've caught the plane" |magazine= Rail |url= https://www.railmagazine.com/trains/new-trains/catch-the-train-and-you-ve-caught-the-plane |access-date= 25 March 2024 }}</ref><ref name=Wolmar>{{cite news |last= Wolmar |first= Christian |date= 3 April 1996 |title= National Express wins Gatwick rail franchise |work= The Independent |url= https://www.independent.co.uk/news/national-express-wins-gatwick-rail-franchise-1303118.html |access-date= 25 March 2024 }}</ref> In the first seven months of the service, the number of passengers travelling by rail to Gatwick Airport went up by 38% and revenue on the route increased by 52%.<ref name=Foster_2014/> Responsibility for running the Gatwick Express was transferred to the [[InterCity (British Rail)|InterCity]] sector of British Rail in April of the following year.{{sfn|Green|Vincent|2014|pp=18-19}} A service from {{rws|Reading}} to Gatwick via {{rws|Guildford}} and Redhill, later branded the [[North Downs Line]], was introduced in May 1980.{{sfn|Jackson|1999|p=102}} A third new route launched by Network SouthEast was the {{rws|Bedford}}{{endash}}Brighton [[Thameslink]] service via the [[Snow Hill tunnel (London)|Snow Hill tunnel]] under central London, which began on 16 May 1988.{{sfn|Jackson|1999|pp=100-101}}{{sfn|Green|Vincent|2014|p=101}}<ref>{{cite news |title= All systems go for Thameslink |date= 13 May 1988 |work= Croydon Advertiser |issue= 6232 |page= 5 }}</ref>

Two major stations on the Brighton Main Line were rebuilt in the early 1990s. A new circular station building at Redhill station, designed by the architecture firm, Troutham & Macasum, was completed towards the end of 1990.{{sfn|Jackson|1999|p=100}}{{sfn|Green|Vincent|2014|p=69}} East Croydon station, designed by Alan Brookes Associates, opened on 19 August 1992.<ref>{{cite news |last= Alford |first= Simon |date= 21 August 1992 |title= BR unwraps its vision of the future |work= Croydon Advertiser |issue= 6455 |page= 3 }}</ref>