London's Metropolitan Railway (MR) amalgamated with other underground railways, tramway companies and bus operators on 1 July 1933, to form the London Passenger Transport Board (LPTB); the MR became the Board's Metropolitan line.
The LPTB cut back services to , closing the Brill and branches, and invested in new rolling stock and improving the railway between Baker Street and Harrow-on-the-Hill, including the extension of the Bakerloo line which took over the Stanmore branch. The outbreak of the Second World War saw these works suspended, and it was not until 1948 that Harrow-on-the-Hill station was enlarged to six platforms.
Steam locomotives were used north of Rickmansworth until the early 1960s, when they were replaced following the electrification of the tracks to Amersham and the introduction of new electric multiple units. London Transport withdrew its service north of Amersham at this time.
In 1988, the route from Hammersmith to Aldgate and Barking was re-designated as the Hammersmith & City line, and the route from and to Shoreditch as the East London line; this left the Metropolitan line as the route from Aldgate to Baker Street and northwards to stations via Harrow, and that designation continues to this day.
History
Metropolitan Railway (1863–1933)
The origins of the Metropolitan line lie with the Metropolitan Railway (MR), the first underground railway built in London. The MR opened a line between Paddington and Farringdon Street in 1863. The line, opened with steam locomotives and gas-lit wooden carriages, was built to connect the capital's mainline railway termini. After forming part of the 'inner circle' (today's Circle line), the railway began to extend out to the suburbs from Baker Street, reaching Harrow in 1880, and eventually as far as , over from Baker Street and the centre of London. The railway started to electrify its routes from 1905. It used electric multiple units on the electrified routes in London, but in order to serve stations on the unelectrified outer lines, coaches were hauled out of London by an electric locomotive that was changed for a steam locomotive en route. After the First World War, the "Metro-land" name was used to promote the new housing estates being built near the railway.
New Works, war and aftermath (1933–48) On 1 July 1933, the MR amalgamated with other underground railways, tramway companies and bus operators to form the London Passenger Transport Board (LPTB). As a result, the MR became the Metropolitan line of London Transport. The LPTB was not interested in running goods and freight services. Carriage of parcels was discontinued on 2 July 1934; Vine Street goods station (near Farringdon station) closed on 30 June 1936, and the London and North Eastern Railway (LNER) took over all freight traffic from 1 November 1937. At the same time the LNER became responsible for hauling passenger trains with steam locomotives north of .
The lines north of to Verney Junction and were closed; the last train to Brill ran on 30 November 1935, and that to and Verney Junction on 2 April 1936. Quainton Road continued to be served by the LNER.
From 1935, the New Works Programme entailed some station rebuilding at places such as Rayners Lane, Eastcote, Ruislip Manor and Uxbridge. However, there was a bottleneck at where four tracks became two for the run through the tunnels to Baker Street. The solution chosen by the LPTB was to extend the Bakerloo line through new tube tunnels from Baker Street to Finchley Road, and for these trains to take over the service to intermediate stations to and the branch to . The old Metropolitan & St. John's Wood Railway stations at St John's Wood Road, Marlborough Road and Swiss Cottage were replaced by new tube stations at St John's Wood and Swiss Cottage. Platform alterations were needed between Wembley Park and Finchley Road, and a flying junction was built at Wembley Park junction. The intention was to enlarge Harrow from four to six platforms, providing dedicated platforms for LNER trains, but this was not completed before the outbreak of the Second World War caused work to be suspended. Construction began in April 1936, and on 2 November 1939 the Bakerloo line served Stanmore for the first time.