Gilles de Kerchove, the EU's counter-terrorism co- ordinator, said that terror networks based in the Middle East like Al Qaeda and Islamic State (ISIS), could begin using the internet to instruct on the use of biological agents.
"If we don't address the grievances which led to the creation of Daesh (ISIS) Sunni grievances against sectarian Shia policies and state violence from [Syrian President] Assad, we are likely to see the resurgence of something that could be Daesh 2.0," Kerchove told a conference organised by the UK-based think tank Royal United Services Institute (RUSI) in London this week.
"Unfortunately, it's probably easier than before for a lone actor to perpetrate an attack with catastrophic consequences."
Kerchove also warned that terrorists could tap into networks of cyber criminals to develop or buy the expertise to launch a devastating cyber-attack.
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Patrick McGuinness, the UK's Deputy National Security Adviser and one of British Prime Minister Theresa May's senior-most security advisers, agreed that all terrorists needed was the "internet and a mindset" to perpetrate global atrocities and it was important to defeat them online.
He said the speed at which people are"brought to violence" was now "almost too fast to catchwithout the most extraordinary intrusive surveillance techniques which are not going to be sustainable or acceptable in a Western democracy."
The UK's security minister, Ben Wallace, told the conference a total of eight planned attacks had been thwarted since the ISIS-inspired attack on the UK Parliament building in Westminster in March this year, bringing the total to 21 since 2013.
"It is not a spike in the threat, but a shift that we are now facing, and that is something we all have to deal with," he added.
Wallace said a new counter-terrorism strategy is set to be unveiled by the UK government in the New Year, to keep "one step ahead of the terrorists".