Prosecutors said the list of targets included the U.S. Embassy in London, two rabbis and the home of London Mayor Boris Johnson. There was also talk of an attack on Parliament, The Daily Telegraph reported.
The men said they were inspired by al-Qaida.
Mohammed Chowdhury, 21, and Shah Rahman, 29, of East London were trailed by investigators as they toured central London on Nov. 28, 2010, prosecutors said. Police said they found the target list in Chowdhury's desk.
Abdul Miah, 25, and his brother Omar Latif, 28, of Cardiff, Wales, also pleaded guilty to taking part in the London Stock Exchange plot.
Five other men, including four from Stoke, England, pleaded guilty to lesser charges. The three groups, which made contact with each other through proselytizing or Internet messaging, met in November and December 2010.
The London and Cardiff groups had wanted to send bombs through the Royal Mail before deciding on a plan to set off bombs in the toilets of the London Stock Exchange. The Stoke group allegedly talked about persuading others to carry bombs into pubs in the English Midlands.
Gurukanth Desai, 30, of Cardiff., pleaded guilty to attending meetings. Mohibur Rahman, 27, from Stoke pleaded guilty to possession of an al-Qaida magazine. Usman Khan, 20, Mohammed Shahjahan, 27, and Nazam Hussain, 26, all from Stoke, pleaded guilty to preparing acts of terrorism.