Editing Chiltern Main Line (section)

===Heyday, decline and rationalisation===
{{More citations needed section|date=June 2011}}
[[File:Seer Green geograph-2456422-by-Ben-Brooksbank.jpg|thumb|right|An ''Ex-''GWR [[GWR 6000 Class|King Class]] locomotive 6008 ''King James II'' hauling a Paddington to Birkenhead Woodside express in 1950]]
[[File:Seer Green station geograph-2400005-by-Ben-Brooksbank.jpg|thumb|right|A {{brc|52}} hauling an express from Paddington to Birkenhead Woodside near {{rws|Seer Green}} in 1962]]

During the heyday of the route, many prestigious trains ran from Paddington to the north-west of England, via the Joint Line; these reached Wolverhampton, {{rws|Shrewsbury}}, {{rws|Wrexham General}}, Chester and Birkenhead Woodside. Various through services from Marylebone to the GCR network also ran via the Joint Line between London and Ashendon Junction.

At [[Transport Act 1947|nationalisation in 1948]], the line passed to the [[Western Region of British Railways]], which continued to operate Paddington-Birmingham-Wolverhampton-Birkenhead fast trains through the 1950s in competition with the [[London Midland Region of British Railways|London Midland Region's]] (LMR) from Euston via the West Coast Main Line (WCML).

The Paddington-Birmingham-Wolverhampton-Birkenhead fast service was increased sharply in frequency to up to 15 trains a day each way from the 1959–60 timetable to compensate for the withdrawal of most London Midlands Region trains during electrification of the WCML.<ref>{{cite news |title=The winter timetables of British Railways: Western Region|work=[[Trains Illustrated]] |publisher=[[Ian Allan Publishing|Ian Allan]] |location=Hampton Court |date=December 1959 |page=584}}</ref> For the same reason, the Chiltern line was used by many trains between Paddington and Birkenhead from 1965.

All local trains were diverted to Marylebone in 1963 and operated by four-car [[British Rail Class 115|Class 115]] [[diesel multiple units]] (DMUs) and the main-line platforms at Greenford, on the New North route between Old Oak Common and Northolt Junction, were closed.

After the GCR main line was closed between {{rws|Calvert}} and {{rws|Rugby Central}} in September 1966, some trains from the South Coast were diverted north of Banbury via the route.  These became the forerunners of today's [[CrossCountry]] services between Birmingham and {{rws|Bournemouth}}.

[[File:Train, Marylebone station, London 3224106.jpg|thumb|right|Class 115 DMUs operated Marylebone – Banbury local services between 1960 and 1992]]

On 6 March 1967,<ref name=rcw>{{cite book |last=Collins |first=Paul|title=Rail Centres: Wolverhampton |publisher=Ian Allan |location=[[London]] |year=1990 |isbn=978-0-7110-1892-1}}</ref> after completion of the WCML electrification, express trains from Paddington to Birmingham/Wolverhampton/Birkenhead were discontinued under ''[[Beeching Axe|The Reshaping of British Railways]]''. The route was downgraded to secondary status, with all but one of the main-line services between London and Birmingham diverted via Oxford. In 1968, the line between Princes Risborough and Aynho Junction was reduced to single track and only a basic two-hourly DMU service between Marylebone and Banbury remained to serve Bicester.<ref name="BLHS">{{cite web |title=Railways |url=https://www.blhs.org.uk/index.php/transport/railways |publisher=Bicester Local History Society |access-date=21 October 2021}}</ref> Through lines were removed from most of those stations which had them, including Denham in 1965, Beaconsfield in 1973 and Gerrards Cross in 1989; the relief lines were lifted between Lapworth and Tyseley. The tunnel between Birmingham Moor Street and Snow Hill was closed on 2 March 1968.<ref name=rcw/> Local services from Leamington and Stratford terminated at Moor Street; the remaining services from Paddington and the South Coast were diverted into New Street. Snow Hill closed completely, along with most of the line to Wolverhampton, on 4 March 1972.<ref name=rcw/>

On 24 March 1974, the line from Marylebone to Banbury transferred from the Western Region to the [[London Midland Region of British Railways|London Midland Region]]; all stations between South Ruislip and Bicester were also transferred to LMR, giving LMR the responsibility of all passenger services out of Marylebone.

In 1977, the Parliamentary Select Committee on Nationalised Industries recommended considering [[Railway electrification in Great Britain|electrification of more of the rail network]] and, by 1979, BR presented a range of options to electrify numerous routes by 2000.<ref name="BR-CPU">{{cite book |author=Anonymous |title=Railway Electrification|date=Winter 1979 |publisher=[[British Railways Board]] (Central Publicity Unit) |pages=0–2, 8}}</ref> Some of these options included the Banbury–Birmingham section of the line, plus the [[Cherwell Valley Line]] and the [[Coventry to Leamington line]].<ref name="BR-CPU"/> Under the [[Premiership of Margaret Thatcher|1979–90 Conservative governments]] that succeeded the [[Callaghan ministry|1976–79 Labour government]], the proposals were not implemented.

The route was considered for partial closure between Marylebone and Northolt Junction in the early 1980s. All services would have run to Paddington, via the New North route; Marylebone station, and all lines leading to it, would have been closed and converted into a bus station. Services to and from Aylesbury would have been taken over by [[London Underground]] and run into [[Baker Street tube station|Baker Street]]. However, these proposals proved impractical and Marylebone was formally reprieved in 1986 (with a press announcement made on 30 April 1986) and the closure proposals rescinded.<ref name=Almostterminal>{{cite web |title=Almost Terminal: Marylebone's Brush With Destruction |url= http://www.londonreconnections.com/2014/near-terminal-case-saving-marylebone-rail-road-conversion/ |website=London Reconnections |access-date=15 September 2015 |date=20 February 2014}}</ref>