Jihadi John and other ISIS extremists are building a network of 'misfits ' around the world who can carry out 'chaotic ' terror attacks with little planning , a senior police officer has warned . Assistant Commissioner Mark Rowley , head of specialist operations at the Metropolitan Police , said ISIS is trying to 'pick up ' potential fighters among 'the vulnerable , people with violent backgrounds , very young people and those with mental health issues ' . Mr Rowley issued the warning of new tactics among Islamist fanatics at the Counter-Terror Expo at Olympia , west London , yesterday . London-born ISIS execution Jihadi John is being used to recruit a network of 'misfits ' around the world , made up of the 'very young , violent and mentally ill ' , a senior police officer has warned . On changing methods of attack , Mr Rowley said : 'We still have groups who are interested in the awful , spectacular attacks that we have seen with Al Qaeda in the past . 'That 's still something we have to be concerned and worried about . But now there 's a much wider range , with chaotic attacks across the world using knives , using vehicles . 'The real aim being to kill and get footage of that to propagate the message and propagate their cause . ' His words echo the case of London teenager Brustholm Ziamani , who was jailed in February for plotting a 'Lee Rigby-style ' attack on a British soldier or policeman . He fell under the spell of the notorious al-Muhajiroun group once fronted by hate preacher Anjem Choudary after being made homeless in London . In 2008 , 22-year-old Nicky Reilly - who had a mental age of 10 - attempted to carry out a suicide bombing in Exeter after he was contacted by extremists online . Assistant Commissioner Mark Rowley said yesterday that the tactics of terror groups are changing . Mr Rowley said there had been a 'step-change ' in the scope and scale of terror threats . Citing the rise of ISIS in Syria and northern Iraq , compared to existing terror strongholds in Afghanistan , Somalia and Yemen , he said : 'It 's a much easier area to get to . It 's not far from budget holiday trips to Turkey and Greece that those terror groups travel to , to exploit . ' More than 600 British jihadists have travelled to join ISIS , with half returning to pose a threat on UK streets . But Mr Rowley said around 50 per cent did not have terror links before flying to Syria . Instead , many had been radicalised via propaganda on social media , by extremists , hate preachers and fighters such as Jihadi John - real name Mohammed Emwazi . Branding ISIS a cult , Mr Rowley added : 'It is actually looking to inspire people to support their cause . 'They 're developing that with a very , very determined approach to exploiting social media and propaganda . ' London teenager Brustholm Ziamani ( left ) was picked up by Islamic extremists after he was kicked out of his home . Mentally ill Nicky Reilly ( right ) was also goaded into carrying out a nail bomb attack in 2008 . Mr Rowley added : 'We have terrorist groups now able , from relatively safe environments in ungoverned space of broken areas of the country , to reach into communities in the UK and influence people to act in their name to commit terrorist act . That is a fundamental difference in the challenge the UK is facing . ' The speech came amid reports that ISIS chief Abu Bakr al-Bagdadi has been injured in an air strike in Iraq and is no longer in control of the group . It is said his deputies in the organisation have been running day-to-day activities while he recovers , following the reported attack on March 18 . Reilly hoped to kill or wound as many diners as he could with the crude nail bomb he had made . In a display of the tactics outlined by Mr Rowley , a man with learning difficulties was coaxed into carrying out a botched restaurant bombing in 2008 . Nicky Reilly , from Plymouth , tried to blow himself up in a busy Giraffe restaurant in Exeter after accessing an extremist website online . He was preparing the nail bomb device in the restaurant 's toilet when it went off in his hands , injuring him but no one else . Deputy Chief Constable Tony Melville , who investigated the case , said at the time : 'He was preyed upon , radicalised , and taken advantage of . ' Reilly 's mother Kim told how he had a mental age of 10 and suffered from mental illness . She said he was an 'easy target , easy prey ' for radicalisation . Judge Mr Justice Calvert-Smith , who jailed Reilly for life for attempted murder , said after the trial : 'There is evidence from materials seized that he became increasingly drawn to violent action in support of fellow Muslims in revenge for perceived persecution , and to the idea of himself personally becoming a martyr . '
Met Office Assistant Commissioner says fanatics ' tactics have changed . Rather than large-scale 9/11-style attacks , smaller cells are now forming . al-Muhajiroun uses videos like those featuring Jihadi John to inspire followers . Extremists are now targeting the mentally ill and very young , he said .