This is what we found on Wikipedia regarding the London Zoo: Entry Ticket:

London Zoo, previously known as ZSL London Zoo or London Zoological Gardens and sometimes called Regent's Park Zoo, is the world's oldest scientific zoo. It was opened in London on 27 April 1828 and was originally intended to be used as a collection for scientific study. In 1831, the Tower of London menagerie animals were transferred to the zoo's collection. It was opened to the public in 1847. At its peak, the Zoo attracted over 3 million annual visitors and exhibited over 900 species. As of 2025, London Zoo still houses more than 8,000 individuals from over 300 species, making it one of the largest zoological collections in the United Kingdom.

It is managed under the aegis of the Zoological Society of London (established in 1826) and is situated at the northern edge of Regent's Park, on the boundary line between the City of Westminster and the borough of Camden (the Regent's Canal runs through it). The Society also has a more spacious site at Whipsnade Zoo in Bedfordshire where larger animals, such as elephants and rhinos, have been moved. As well as being the first scientific zoo, London Zoo also opened the first reptile house (1849), the first public aquarium (1853), the first insect house (1881) and the first children's zoo (1938).

The Society receives no state funding and relies on 'Fellows' and 'Friends' memberships, entrance fees, venue hire, and sponsorship to generate revenue.