Britain's security services are investigating 30 British-based Islamist terrorist plots, and watching over 1,600 suspected terrorists and 200 terror networks, the director-general of MI5 reported Thursday. In a rare public address, Dame Eliza Manningham-Buller said there had been an 80 percent rise in case work since January of groups in Britain "who are actively engaged in plotting or facilitating terrorist acts here and overseas." Home Secretary John Reid gave the MI5 chief permission to brief the invited audience at London's Queen Mary College, on the threat Britain faces from al-Qaida and homegrown Islamist terrorism. It was Manningham-Buller's third public briefing on the terror threat since the July 7, 2005 London underground bombings. "I do not speak in this way to alarm, nor as the cynics might claim, to enhance the reputation of my organization but to give the most frank account I can of the al-Qaida threat to the UK," Manningham-Buller said. "The threat is serious, is growing and will, I believe, be with us for a generation," she said, noting terrorist recruiters could draw from a pool of up to 100,000 British Muslims, whom surveys said sympathized with the July 7 terror attacks. "The extremists are motivated by a sense of grievance and injustice driven by their interpretation of the history between the West and the Muslim world," she said. Many Muslim teens, some still in school, were being radicalized across the country, with some "groomed to be suicide bombers," Manningham-Buller said. The terror plots "often have links back to al-Qaida in Pakistan," she said, "and through those links al-Qaida gives guidance and training to its largely British foot soldiers here on an extensive and growing scale," across Europe and in Canada. "Today we see the use of homemade improvised explosive devices. Tomorrow's threat may include the use of chemicals, bacteriological agents, radioactive materials and even nuclear technology," the MI5 chief said. "It is a sustained campaign, not a series of isolated incidents. It aims to wear down our will to resist," she said. In an address given at the Royal United Services Institute the same morning, Foreign Secretary Margaret Beckett said that unlike Britain's battle with Irish terrorism, the conflict with militant Islam was ideological and was not connected to "a single national cause or still more to an achievable political demand." It was a "cult" based "on a pseudo-religious vision of a transformed world." "That is how it is able to persuade a young Briton, born into our tolerant, democratic society to blow himself up on a crowded commuter train or bus. We need to address that warped vision head- on," Beckett said. Claims the UK's foreign policy was "anti-Islamic," were "ridiculous nonsense, even if it is dangerous nonsense," Beckett said at a symposium on "transnational terrorism." "Our foreign policy is simply not based on religion. It is based on our values and on our strategic interests. Both our values and our strategic interests lead us to want a safer, more just and more prosperous world for all," she said. At a press conference with the New Zealand prime minister at Downing Street on November 10, Prime Minister Tony Blair backed his security chief's warning. "This is a threat that has grown up over a generation," Blair said. In addition to tougher security laws, Britain must "take on and combat the poisonous propaganda of those people that warp and pervert the minds, particularly of younger people," he said. The prime minister was optimistic that the ideological war would be won. "Democracy, and tolerance, and liberty and respect for people of other faiths are the values that will defeat those values of hatred and division and sectarianism," Blair said. The struggle will be "very long and deep," he conceded, but we must, nonetheless, "take the fight to those that want to entice young people into what is in the end not just something that is wicked and violent, but something that is utterly futile." The government is expected to announce new anti-terrorist legislation in the Queen's speech at the state opening of Parliament on Wednesday.