Four British men allegedly inspired by the words of a US-born Muslim religious leader have pleaded guilty to involvement in a plot to bomb the London Stock Exchange at Christmas time in 2010.

The men were among nine defendants facing trial in London over an alleged al-Qaeda-inspired plot to attack several prominent targets. All had initially pleaded not guilty to all the charges.

But on Wednesday four of them pleaded guilty at Woolwich Crown Court to involvement in the stock-exchange attack plan, and the five others to lesser charges.

Mohammed Chowdhury, Shah Rahman, Gurukanth Desai and Abdul Miah, all aged between 21 and 30, admitted to preparing for acts of terrorism by planning to plant an improvised explosive device in the toilets of the London Stock Exchange.

Andrew Edis, the prosecution lawyer, accepted that the men had not planned to kill anyone.

"Their intention was to cause terror and economic harm and disruption," he said. "But their chosen method meant there was a risk people would be maimed or killed."

Plot's 'lynchpin'

Chowdhury, from London, was described by prosecutors as the "lynchpin" of the plot.

His lawyer, Christopher Blaxland, said Chowdhury admitted planning 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".

The other five defendants admitted attending planning meetings, fundraising for the attack or possessing copies of the al-Qaeda magazine, Inspire.

Prosecutors said they had not made any bombs or set dates for the attacks.

They said the men were not members of al-Qaeda but had been inspired by the network and the sermons of its Yemen-based American-born Anwar al-Awlaki, who was killed last year in a US drone attack.

Edis said the nine defendants "were implementing the published strategy"of Al-Qaeda in the Arabian Peninsula.

The suspects were arrested in London, Cardiff and Stoke-on-Trent in central England, in what police called the biggest anti-terror raid in two years.

Prosecutors said they plotted to send mail bombs to various targets in the run-up to Christmas and had discussed launching a "Mumbai-style" attack - referring to the bomb blasts and shootings that killed 166 people in India's financial centre in 2008.

Under surveillance

The nine defendants were accused of agreeing on targets, discussing materials and methods, and researching files "containing practical instruction for a terrorist attack".

The men held planning meetings, researched bomb-making and scouted out locations including parliament, Westminster Abbey and the London Eye Ferris wheel - not knowing that they were under police surveillance and that their homes and cars had been bugged.

A handwritten target list found at one of the defendant's homes listed the names and addresses of Boris Johnson, the London mayor; two rabbis; the US embassy; and the stock exchange.

The defendants will be sentenced next week, but the judge has already told Chowdhury he will receive 18.5 years and Rahman 17 years. They are likely to serve half that time before being eligible for parole.

London has been targeted several times by plotters affiliated with or inspired by al-Qaeda. In July 2005, four suicide bombers killed 52 commuters on three London underground trains and a bus.

A year later, US and British intelligence officials thwarted one of the largest plots yet - an alleged plan to explode bombs on nearly a dozen trans-Atlantic airliners.