LONDON — Long before bombings ripped through London on Thursday, Britain had become a breeding ground for hate, fed by a militant version of Islam.

For two years, extremists like Sheik Omar Bakri Mohammed, a 47-year-old Syrian-born cleric, have played to ever-larger crowds, calling for holy war against Britain and exhorting young Muslim men to join the insurgency in Iraq. In a newspaper interview in April 2004, he warned that "a very well-organized" London-based group, al-Qaida Europe, was "on the verge of launching a big operation" here.

In a sermon attended by more than 500 people in a central London meeting hall last December, Mohammed vowed that if Western governments did not change their policies, Muslims would give them "a 9/11, day after day after day."

If London became a magnet for fiery preachers, it also became a destination for men willing to carry out their threats. For a decade, the city has been a crossroads for would-be terrorists who used it as a home base, where they could raise money, recruit members and draw inspiration from the militant messages.

Among them were terrorists involved in attacks in Madrid, Casablanca, Saudi Arabia, Israel and in the Sept. 11 plot. Zacarias Moussaoui, the only man charged in the United States in the 9/11 attacks, and Richard C. Reid, the convicted shoe-bomber, both prayed at the Finsbury Park mosque in north London. The mosque's former leader, Abu Hamza al-Masri openly preached violence for years before the authorities arrested him in April 2004.

Although Britain has passed a series of anti-terrorist and immigration laws and made nearly 800 arrests since Sept. 11, 2001, critics have charged that its deep tradition of civil liberties and protection of political activists have made the country a safe haven for terrorists. The British government has drawn particular criticism from other countries over its refusal to extradite terrorism suspects, including one man who was convicted for his role in the deadly Casablanca terrorist attacks in 2003.

For years, there was a widely held belief that Britain's tolerance helped stave off any Islamic attacks at home. But the anger of London's militant clerics turned on Britain after it offered unabashed support for the American-led invasion of Iraq. On Thursday morning, an attack long foreseen by worried counterterrorism officials became a reality.

"The terrorists have come home," said a senior intelligence official based in Europe, who works often with British officials. "It is payback time for a policy that was, in my opinion, an irresponsible policy of the British government to allow these networks to flourish inside Britain."