"More broadly, as Islamist territory in the Middle East continues to shrink under various assaults, Europe is preparing for the return of large numbers of radicalised nationals who fought alongside IS and other groups. Authorities believe that as many as 760 British nationals could return to the UK. Such individuals, trained, experienced, and perhaps better supported by the wider jihadist network, are likely to pose a far greater threat than lone-wolf actors. Former fighters will have the potential to enlist militants into new domestic networks and share knowledge of terrorist tactics, bomb construction and the acquisition of weapons, exacerbating the current terrorist threat considerably and creating the conditions for more frequent high-profile, mass-casualty attacks."
https://www.red24.com/members/indepth/uk_terrorism_attacks.php
"More broadly, as Islamist territory in the Middle East continues to shrink under various assaults, Europe is preparing for the return of large numbers of radicalised nationals who fought alongside IS and other groups. Authorities believe that as many as 760 British nationals could return to the UK. Such individuals, trained, experienced, and perhaps better supported by the wider jihadist network, are likely to pose a far greater threat than lone-wolf actors. Former fighters will have the potential to enlist militants into new domestic networks and share knowledge of terrorist tactics, bomb construction and the acquisition of weapons, exacerbating the current terrorist threat considerably and creating the conditions for more frequent high-profile, mass-casualty attacks."