The Underground Electric Railways Company of London Limited (UELR), sometimes referred to simply as the Underground Electric Railway, was formed in 1902 by American financier Charles Yerkes and incorporated not only his existing company, the Metropolitan District Electric Traction Company, but also the unbuilt Baker Street and Waterloo Railway (B&SWR), Charing Cross, Euston and Hampstead Railway (CCE&HR) and Great Northern, Piccadilly and Brompton Railway (GNP&BR). Due to Yerkes’ financial arrangements he was able to raise enough funds to not only undertake the construction of these lines but also to convert the District line from steam to electric traction, making use of the Lots Road Power Station for all of them.

In October 1905, the electrification of the District Railway was completed and the following year the B&SWR and GNP&BR were both opened. In 1907 the CCE&HR was also opened which meant that all the subsidiaries were operating by this time. Although they all shared directors, technology and, in the case of the newly built lines, architectural styles they were all operated as separate companies, only being linked by being part of the Underground Electric Railways holding company. As a result of this structure the individual lines struggled to make enough to pay back the money they had borrowed to compete construction. Partly in an effort to remedy this situation a joint fare system was introduced in 1907.

Further efforts to improve this were implemented in 1908 when all the lines began to be marketed under the single Underground brand. This culminated in 1909 when the London Electric Railway Amalgamation Act was put forward. This proposed the merger of the three tube companies to form the London Electric Railway Company. The act passed in 1910 and the new company was majority owned by the Underground Electric Railways Company of London Limited. The Metropolitan District Railway was not included in this and remained a separate company under the direct control of the UERL.

The group would further expand on 1st January 1912 when it would purchase the London General Omnibus Co (LGOC). At the time this was a very profitable company it was therefore possible to use the money it generated to subsidies the struggling railway operations. At the same time the bus building section of LGOC was separated from the operational department to form Associated Equipment Co, later known as AEC. The same year would also see the company form London and Suburban Traction Company, in partnership with British Electric Traction Co, to take over the tram services of London United Tramways, Metropolitan Electric Tramways and South Metropolitan Electric Tramways and Lighting Co. In 1913 the UERL would further expand when it purchased the City and South London Railway and the Central London Railway.

During the First World War many of the company’s buses were commandeered by the government to provide transport for the British Army in France and their other activities were limited due to controls imposed on the company’s facilities. Following the end of the conflict the management of the companies was further consolidated and other improvements were implemented in the form of new rolling stock and the rebuilding of some stations.

The 1920s would see some difficulties for the group as it would face increased competition from small unregulated bus operators that were able to undercut the more established operators. In 1922 Sir Fredrick Sykes would be appointed as the director of the UERL and it would also begin to lobby for greater regulation of the London public transport sector. Further attempt to improve the situation would be also be implemented in 1926 when the group would begin to acquire small competitors. Finally, in 1930 Green Line Coaches Ltd was created to reflect the development of motor coaches, that allowed for routes to be extended into the countryside and was operated as part of the LGOC.

On 1st July 1933 the London Passenger Transport Board was formed to take over the buses, trams and underground railways in the London area. The board had been formed by the London Passenger Transport Act and took over the 92 existing transport and associated undertakings. This included the companies that made up the Underground Electric Railways Company of London Limited, although it would sell of the shares in AEC that it inherited so that it could be operated as a separate entity. The move would also see the beginning of the London Transport name being used.