Four British men have pleaded guilty this morning to involvement in an al-Qaida inspired plot to bomb the London Stock Exchange.

The men were among nine defendants facing trial in London over an alleged plot to attack the exchange and several other high-profile targets in December 2010. All had initially pleaded not guilty to all the charges against them.

But on Wednesday four of the defendants pleaded guilty at Woolwich Crown Court to involvement in the Stock Exchange plot, and the five other British citizens to lesser charges.

The suspects, aged between 20 and 30, were arrested in London, Cardiff and Stoke-on-Trent in central England, in what police called the biggest anti-terror raid for two years.

Prosecutors said they planned to send mail bombs to various targets in the run-up to Christmas 2010 and had discussed launching a “Mumbai-style” atrocity — referring to the bomb blasts that killed 166 people in India’s financial center in 2008.

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

A handwritten target list found at one of the defendant’s homes listed the names and addresses of London Mayor Boris Johnson, two rabbis, the American Embassy and the Stock Exchange.

Mohammed Chowdhury, 21; Shah Rahman, 28; Gurukanth Desai, 30; and Abdul Miah, 25, all admitted preparing for acts of terrorism by planning to plant an improvised explosive device in the toilets of the London Stock Exchange.

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

They will be sentenced next week.