Four men inspired by al-Qaeda have admitted planning to detonate a bomb at the London Stock Exchange, according to the BBC.
Mohammed Chowdhury, Shah Rahman, Gurukanth Desai, and Abdul Miah pleaded guilty to engaging in conduct in preparation for acts of terrorism.
The men, from London and Cardiff, were arrested in December 2010 and were set to stand trial at Woolwich Crown Court.
Five other men have pleaded guilty to other terrorism offences and all nine will be sentenced next week.
The men, who are all British nationals, had been inspired by the preachings of the recently-killed radical extremist Anwar Al-Awlaki.
The plot revolved around sending five mail bombs to various targets in the run-up to Christmas 2010.
A hand-written target list discovered at the home of one of the men listed the names and addresses of London Mayor Boris Johnson, two rabbis, the US embassy and the Stock Exchange.
The conspiracy was stopped by undercover anti-terror police before firm dates could be set for attacks.
The court heard that Chowdhury, 21, and his London accomplice Rahman, 28, were followed by undercover detectives on 28 November 2010, observing Big Ben, Westminster Abbey, the London Eye and the Palace of Westminster.
Chowdhury, of Stanliff House, Tower Hamlets and Rahman, of St Bernard's Road, Newham, admitted preparing for acts of terrorism by planning to plant an improvised explosive device in the toilets of the London Stock Exchange.
The men admitted the crime after a hearing was held to give them an indication of their maximum sentences, the BBC reports.
Chowdhury was told by judge Mr Justice Wilkie that he would receive 18-and-a-half years, while Rahman was told he would receive a maximum of 17 years.
The four men aimed to plant the bomb "with the obvious attendant risk but without any intention to cause death or even injury, but with the intention to terrorise, damage property and to cause economic damage," Chowdhury's barrister, Christopher Blaxland QC, told the court.
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