The Charing Cross, Euston and Hampstead Railway (CCE&HR), also known as the Hampstead tube, was a railway company established in 1891 that constructed a deep-level underground "tube" railway in London.] Construction of the CCE&HR was delayed for more than a decade whilst funding was sought. In 1900, it became a subsidiary of the Underground Electric Railways Company of London (UERL) controlled by American financier Charles Yerkes. The UERL quickly raised the funds, mainly from foreign investors. Various routes were planned but a number of these were rejected by Parliament. Plans for tunnels under Hampstead Heath were authorised, despite opposition by many local residents who believed they would damage the ecology of the Heath.
The Wikipedia page is [1] and the London Remembers page is [2].