Railways in underground:

In 1854 an Act of Parliament was passed approving the construction of an underground railway between Paddington Station and Farringdon Street via King's Cross which was to be called the Metropolitan Railway. The Great Western Railway (GWR) gave financial backing to the project when it was agreed that a junction would be built linking the underground railway with their mainline terminus at Paddington. GWR also agreed to design special trains for the new subterranean railway.
Construction was delayed for several years due to a shortage of funds. The fact that this project got under way at all was largely due to the lobbying of Charles Pearson, who was Solicitor to the City of London Corporation at the time. Pearson had supported the idea of an underground railway in London for several years. He advocated plans for the demolition of the unhygienic slums which would be replaced by new accommodation for their inhabitants in the suburbs, with the new railway providing transportation to their places of work in the city centre. Although he was never directly involved in the running of the Metropolitan Railway, he is widely credited as being one of the first true visionaries behind the concept of underground railways. And in 1859 it was Pearson who persuaded the City of London Corporation to help fund the scheme. Work finally began in February 1860, under the guidance of chief engineer John Fowler. Pearson died before the work was completed.
The Metropolitan Railway opened on 10 January 1863.[4] Within a few months of opening it was carrying over 26,000 passengers a day.[8] The Hammersmith and City Railway was opened on 13 June 1864 between Hammersmith and Paddington. Services were initially operated by GWR between Hammersmith and Farringdon Street. By April 1865 the Metropolitan had taken over the service.
On 23 December 1865 the Metropolitan's eastern extension to Moorgate Street opened. Later in the decade other branches were opened to Swiss Cottage, South Kensington and Addison Road, Kensington (now known as Kensington Olympia). The railway had initially been dual gauge, allowing for the use of GWR's signature broad gauge rolling stock and the more widely used standard gauge stock. Disagreements with GWR had forced the Metropolitan to switch to standard gauge in 1863 after GWR withdrew all its stock from the railway. These differences were later patched up, however broad gauge was totally withdrawn from the railway in March 1869.