Before nationalisation

The railways previously passed over each other without a junction, until the merger of the London, Chatham and Dover Railway (LCDR) and the South Eastern Railway (SER) on 1 January 1899 meant it made operational sense to build connections between the previously disparate networks.^[1] The first connection, the "down" Bickley Loop, opened on 8 September 1902 with a length of ¾ miles (1 km).^[1] The reverse connection opened six days later.^[1] These connecting loops allowed trains to/from London Victoria to operate on the former SER line.^[1] The west and east ends of the loops became known as Bickley Junction and Orpington Junction respectively, named after the next stations on the line at the time.^[1] The corresponding connection (the Chislehurst Loops), allowing transfer of Charing Cross trains to/from the Chatham line was, opened on 19 June 1904.^[1]

From 1925 the Southern Railway — which had been formed in 1923 assuming the junction's previous owners — began to electrify the routes through the junction.^[1] The first to be installed with a third rail was the Bickley Loop, on 12 July 1925.^[1] This was followed by full electrification between Orpington Junction and Charing Cross on 28 February 1926. In connection with this wave of electrification, a three-storey red brick substation was installed, immediately to the north of the Chatham line and west of the Charing Cross line.^[1]

The next electrification did not take place until 1935, when on 6 January the Chislehurst Loops became live along with the section of the line between Bickley and Swanley.^[1] Electrification was further extended to Gillingham on 2 July 1939.^[1]

In the meantime, a new station had been opened at Petts Wood, ⅓ mile (0.5 km) south of Orpington Junction, on 9 July 1928.^[1] This eventually led to the renaming from Orpington Junction to Petts Wood Junction on 8 July 1936, in keeping with the practice of naming a junction after its closest station.^[1]

The last development of the junction under the administration of the Southern Railway came in 1941, when bomb damage to a wooden signal box required its replacement with an austere flat-roofed brick construction.^[1] The robust design of the new edifice was in reaction to the continued air raid threat.^[1]

After nationalisation

Following the nationalisation of railways in Britain in 1948, major modification of the network took place.^[2] Chislehurst Junction benefited in the form of the 1959 Kent Coast Electrification programme, which saw the Victoria-Chatham line quadrupled between Bickley and Swanley.^[2] Semaphore signals were replaced throughout with colour light signals, which brought about the need for a "power box" at Chislehurst Junction, situated between the two mainline routes, on the west side of the South Eastern Main Line.^[2] This assumed the functions of the mechanical signal boxes at Bickley, Chislehurst and Petts Wood junctions on 31 May 1959.^[2]

As part of the same project, work was undertaken to modify the junctions in order to increase the speed limit.^[2] The Bickley Loops were realigned to allow trains to pass through at 50 mph (80 km/h), instead of 30 mph (48 km/h) previously.^[2] This realignment also required the reconstruction of the bridge which took the South Eastern Main Line over the Down Bickley Loop.^[2]

The next modification to the signalling arrangement came in 1976, when the multi-panel London Bridge signal box became operational.^[2] This allowed the reversible operation of the Down Chislehurst Loop.^[2] The 1959-"power box" remained the primary control point for these lines in this area until 12 June 1983.^[2] This date saw the expansion of Victoria Signalling Centre's scope of control as far as the boundary of Rochester signal box.^[2] Chislehurst Junction signal box retained control over the South Eastern Main Line until 1993, when it was taken over as part of the gradual implementation of Ashford Signalling Centre.^[2] Meanwhile, in 1992/1993, the "Up" and "Down" Bickley Loops were doubled to accommodate Eurostar operations, which began in earnest on 14 November 1994.^[2] The new Down Slow Bickley Loop shares the same alignment as the Up Chislehurst where they pass under the South Eastern Main Line.^[2] This created a new junction named Hawkwood Junction.^[2]