In a first-of-its-kind public hearing, the chiefs of British intelligence agencies talked about the serious terror threats still facing their country and the world. They also touched upon "the very damaging" impact of the US intelligence agent Edward Snowden's leaks. Chief of British Security Service (MI5), which is in charge of protecting British national security against threats from espionage, terrorism and sabotage, Andrew Parker told members of the parliament's Security and Intelligence Committee members that a total of 34 terror plots had been foiled since 2005 including "one or two" plots aimed at causing mass casualties. "(There are still) several thousand individuals in this country who I would describe as supporting violent extremism or are engaged in it," Parker said. "The vast majority of plots come from people who live here." He added that some plots aimed to be at least as big as 7/7, 2005 terror attacks and that "Spectaculars are still in the minds of terrorists." He warned about the growth of what he described as "terrorist tourism", where British nationals travel abroad for training before return to the UK to plot attacks, with the civil war in Syria currently proving a magnet for those seeking "jihadi" activity among groups linked to Al-Qaeda. "Syria has become a very attractive place for people to go for that reason - those who support or sympathise with the Al Qaeda ideological message," he said. "We've seen low hundreds of people from this country go to Syria for periods and come back - some large numbers are still there - and get involved in fighting. "This is partly because of the proximity of Syria and the ease of travel there, but also because it is attractive as what they would see as a jihadi cause." Meanwhile, Head of the Secret Intelligence Service (MI6) Sir John Sawers told the committee that Edward Snowden's leaks have been "very damaging" and have put operative's lives at risk. "The leaks from Snowden have been very damaging, they've put our operations at risk," Sawers said. "It's clear that our adversaries are rubbing their hands with glee, Al-Qaeda is lapping it up." For his part, Head of the Government Communications Headquarters (GCHQ) Sir Iain Lobban said that activists in the Middle East and "closer to home" had been monitored discussing ways of switching away from communications they "now perceived as vulnerable" after Snowden's leaks. Responding to a question about using foreign intelligence bodies to gather information from the internet to circumvent UK laws, Lobban said his agency has acted within the law. He also denied claims of complicit in torture of terrorism suspects overseas. "I don't accept the allegations that have been made against us ... we're absolutely clear we only operate within the framework of the law," he said. Lobban, however, admitted cooperation with security agencies of countries with mixed human rights records. "There are some countries which have mixed human rights records and we seek clear assurances that when we provide intelligence it will be used lawfully and if anyone is detained or questioned as a consequence of our intelligence, it is done to our standards."