Editing Great Western Main Line (section)

===British Rail era===
Unlike the other BR regions, which introduced [[diesel-electric]] locomotives, the [[Western Region of British Railways|Western Region]], to which the GWML belonged, decided to procure a complete range of [[diesel-hydraulic]] locomotives to fulfil its [[List of British Rail power classifications|type 1 to type 4]] power requirements. These included the [[British Rail Class 42|''Warship'']] locomotives, which were based on proven [[West German]] designs, the British-designed [[British Rail Class 14|Class 14]], [[British Rail Class 35|''Hymek'']] and [[British Rail Class 52|''Western'']] types. However, these were all eventually withdrawn and replaced with more standard British Rail diesel-electric classes such as the [[British Rail Class 37|Class 37]] and [[British Rail Class 47|Class 47]].

During the 1970s, the line speed of the GWML was upgraded to permit faster operations; this work was in preparation for the introduction of the [[InterCity 125]] high speed train (HST).<ref name='EarlyHighspeedBR'>{{cite journal |title = High speed track on the Western Region of British Railways |last = Collins |first = R.J. |journal = Proceedings of the Institution of Civil Engineers |year = 1978 |volume = 64 |issue = 2 |pages = 207–225 |publisher = [[Institution of Civil Engineers]] |doi = 10.1680/iicep.1978.2755 |language = en-GB}}</ref><ref name=bbc1976>{{cite news |title = New train speeds into service |url = http://news.bbc.co.uk/onthisday/hi/dates/stories/october/4/newsid_2486000/2486817.stm |access-date = 15 May 2019 |work = BBC News |date = 4 October 1976 |language = en-GB}}</ref> The HST brought about considerable improvements in service and reduced journey times.<ref>{{Cite news |last1 = Owen |first1 = A.D. |last2 = Phillips |first2 = G.D.A. |publisher = [[University of Bath]] |title = The Characteristics of Railway passenger demand |page = 234 |url = http://www.bath.ac.uk/e-journals/jtep/pdf/Volume_XX1_No_3_231-253.pdf |language = en-GB}}</ref><ref>{{cite news |url = http://news.bbc.co.uk/1/hi/england/berkshire/5407016.stm |title = High Speed Train marks 30 years |work = BBC News |access-date = 29 April 2009 |date = 4 October 2006 |first = Joe |last = Campbell |language = en-GB}}</ref>

In 1977, the Parliamentary Select Committee on Nationalised Industries recommended considering electrification of more of Britain's rail network and, by 1979, British Rail had presented a range of options that included electrifying the line from Paddington to Swansea by 2000.<ref>{{cite book |title = Railway Electrification |date = Winter 1979 |publisher = [[British Railways Board]] (Central Publicity Unit) |pages = 0–2, 8}}</ref> Under the [[Premiership of Margaret Thatcher|1979–90 Conservative governments]] that succeeded the [[Callaghan ministry|1976–79 Labour government]], the proposal was not implemented.

In the mid-1990s, the line between London Paddington and [[Hayes & Harlington railway station|Hayes & Harlington]] was electrified as part of the [[Heathrow Express]] scheme, which was officially launched in June 1998.<ref>{{Cite web |title = Heathrow Express |url = https://www.railway-technology.com/projects/heathrow-express/ |access-date = 30 June 2020 |website = Railway Technology |language = en-GB |archive-date = 15 August 2018 |archive-url = https://web.archive.org/web/20180815045612/https://www.railway-technology.com/projects/heathrow-express/ |url-status = live}}</ref><ref>{{cite news |date = 23 June 1998 |title = Heathrow Express takes off |url = http://news.bbc.co.uk/1/hi/uk/118180.stm |url-status = live |archive-url = https://web.archive.org/web/20201220201437/http://news.bbc.co.uk/2/hi/uk_news/118180.stm |archive-date = 20 December 2020 |access-date = 6 August 2016 |work = BBC News |language = en-GB}}</ref>