Four British Islamists inspired by a former Al-Qaeda leader Anwar al-Awlaqi admitted in court on Wednesday to plotting to blow up the London Stock Exchange in 2010.
The men belonged to a group of fundamentalists who planned a spate of mail bomb attacks during the run-up to Christmas that year and discussed launching a "Mumbai-style" atrocity, prosecutors said.
Mohammed Chowdhury, 21, and Shah Rahman, 28, both from London, admitted preparing for acts of terrorism by planning to plant an improvised explosive device (IED) in the toilets of the London Stock Exchange
Brothers Gurukanth Desai, 30, and Abdul Miah, 25, both from the Welsh capital Cardiff, admitted the same count at a London court.
Five other men, four from the central English city of Stoke and another from Cardiff, admitted lesser terror offences.
They will all be sentenced from Monday next week.
Police Deputy Assistant Commissioner Stuart Osborne, senior national coordinator for counter-terrorism, welcomed the guilty pleas, saying the case had been "the largest counter-terrorism operation of 2010".
Police found a handwritten target list at the home of one of the defendants that included the Stock Exchange, Mayor of London Boris Johnson, two rabbis and the US embassy in London.
Detectives also followed Chowdhury and Rahman observing Big Ben, Westminster Abbey, the London Eye and the Houses of Parliament, on November 28, 2010.
Undercover officers stopped the group before they could set firm dates for the attacks, and despite possessing a guide to bomb-making in Al-Qaeda magazine "Inspire" the men did not reach the point of making any explosive devices.
However, prosecutors said they posed a serious threat, not just to the British capital but also to Stoke, where the group talked about leaving homemade bombs in pub toilets.
They also talked about travelling to a terrorism training camp in Kashmir.
They were not members of Al-Qaeda but prosecutors said the defendants were inspired by the terror network and specifically Awlaqi, a suspected leader of the group in Yemen who was killed in September in what is thought to have been a US drone strike.
The nine men "were implementing the published strategy of AQAP" (Al-Qaeda in the Arabian Peninsula, the group's deadliest global branch), said prosecution lawyer Andrew Edis.
He conceded that the four men involved in the London Stock Exchange plot had not intended to hurt anyone.
"Their intention was to cause terror and economic harm and disruption. But their chosen method meant there was a risk people would be maimed or killed," he told the court.
The group, who met because of their membership of various extremist Islamic groups, had originally challenged the charges against them and were due to stand trial, but at the 11th hour they changed their pleas to guilty.
The November 2008 attacks in Mumbai saw 10 heavily-armed Islamist gunmen storm targets including luxury hotels, a Chabad centre and a train station in nearly three days of violence that killed 166 people.
Among the other defendants in the London trial, Usman Khan, 20, Mohammed Shahjahan, 27, and Nazam Hussain, 26, all of Stoke, admitted attending operational meetings in parks in Wales last year
Omar Latif, 28, from Cardiff, admitted attending the meetings with the intention of assisting others to prepare or commit acts of terrorism.
Mohibur Rahman, 27, from Stoke, admitted being in possession of two editions of "Inspire" for terrorist purposes.