[1] Within the first year of opening it became apparent to the management and investors that the estimated passenger numbers for the GNP&BR and the other UERL lines were over-optimistic.

Today, the GNP&BR's tunnels and stations form the core central section of the London Underground's Piccadilly line.

In November 1896 notice was published that a private bill was to be presented to Parliament for the construction of the Brompton and Piccadilly Circus Railway (B&PCR).

[4] Following parliamentary approval, the bill received royal assent as the Brompton and Piccadilly Circus Railway Act 1897 (60 & 61 Vict.

[7] The DR operated a steam railway, running in cut and cover tunnels, and planned to ease congestion along its heavily used route by constructing an express line with just a single intermediate station at Charing Cross (now Embankment).

[9] When the London County Council planned the construction of Kingsway and Aldwych, Stanhope Street was scheduled for demolition so the southern terminus was relocated to the junction of the two new roads.

Foreign investors came to the rescue of the DR, B&PCR and GN&SR: American financier Charles Yerkes, who had been lucratively involved in the development of Chicago's tramway system in the 1880s and 1890s, saw the opportunity to make similar investments in London.

[note 4] With the companies under his control, Yerkes established the UERL to raise funds to build the tube railways and to electrify the DR.

[note 5] Further share issues followed, which raised a total of £18 million by 1903 (equivalent to approximately £2.44 billion today)[14] for use across all of the UERL's projects.

[note 6] During the progress of their 1896 bills through parliament, the DR and the B&PCR established a relationship through a successful joint campaign of opposition to a competing proposal from the City & West End Railway.

The bill received royal assent on 9 August 1899 as the Brompton & Piccadilly Circus Railway (Extensions) Act 1899 (62 & 63 Vict.

The bill also included provisions for the B&PCR to take over responsibility for construction of the section of the DR's deep-level line from South Kensington to Earl's Court, and for a further extension of time.

The section to The Angel was held back, pending the findings of a separate committee which was investigating problems of vibration experienced on the CLR.

The requests for an extension of time and for the powers to build the DR deep-level line from South Kensington to Earl's Court were re-presented.

The GN&SR sought powers for a short extension of about 350 metres (1,148 ft) from its southern terminus, to Temple station on the DR's existing sub-surface line where an interchange was planned.

The GN&SR also sought permission to abandon the section of its route north of Finsbury Park,[note 9] and to transfer its powers and obligations to the B&PCR as part of the merger.

The B&PCR link from Piccadilly Circus to Charing Cross was rejected on the grounds that it involved sharp turns and steep gradients to avoid public buildings in the area.

The eastern extension was to diverge from the main route immediately west of Piccadilly Circus station, which was to be expanded to have east and westbound platforms on both lines.

[49] The bill received royal assent on 4 August 1905 as the Great Northern, Piccadilly and Brompton Railway (Various Powers) Act 1905 (5 Edw.

[53] Work proceeded quickly, enabling the UERL to record in its annual report in October 1904 that 80 per cent of the tunnels had been completed and that track laying was about to begin.

[55] This consisted of two-storey steel-framed buildings faced with dark oxblood red glazed terracotta blocks, with wide semi-circular windows on the upper floor.

[53] Works on the main route were largely complete by the Autumn of 1906,[52] and after a period of test running the railway was ready to open in December 1906.

As a result of the electrification and resignalling of the DR's surface and sub-surface tracks in 1905, the capacity of the existing route was sufficiently increased that the construction of deep-level tunnels east of South Kensington was unnecessary, and the powers were allowed to lapse.

[56] These carriages were built to the same design used for the BS&WR and the CCE&HR, and operated as electric multiple unit trains without the need for separate locomotives.

The UERL's three tube railway companies were still legally separate entities, with their own management, shareholder and dividend structures.

There was duplicated administration between the three companies and, to streamline the management and reduce expenditure, the UERL announced a bill in November 1909 that would merge the Piccadilly, the Hampstead and the Bakerloo Tubes into a single entity, the London Electric Railway (LER), although the lines retained their own individual branding.

[66][note 15] The bill received royal assent on 26 July 1910 as the London Electric Railway Amalgamation Act 1910 (10 Edw.

In an effort to protect the UERL group's income, its chairman Lord Ashfield lobbied the government for regulation of transport services in the London area.

Ashfield aimed for regulation that would give the UERL group protection from competition and allow it to take substantive control of the LCC's tram system; Morrison preferred full public ownership.

[79] Between September 1940 and July 1946, the Strand branch was temporarily closed, its tunnels used to store exhibits from the British Museum as well as serving as an air-raid shelter.